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二元函数z=xy在x+y=1下的极值为___________.
Alice:Hi,Sam!It's nice to see you here.
Sam:Hi,Alice!
Alice:（56）
Sam:To my dorm.
Alice:Great!Could you take this book to Peter?
Sam:（57）Does Peter know what it is for?
Alice:Yes.（58）
Sam:（59）Are you well prepared for it?
Alice:（60）See you tomorrow!
Sam:See you!
A.How about your presentation?
B.He needs it for tomorrow's presentation.
C．l think so.
D．Where are you heading?
E．You are welcome.
F．No problem!
G．What can I do for you?
H．No，thanks!
第（60）题选
Alice:Hi,Sam!It's nice to see you here.
Sam:Hi,Alice!
Alice:（56）
Sam:To my dorm.
Alice:Great!Could you take this book to Peter?
Sam:（57）Does Peter know what it is for?
Alice:Yes.（58）
Sam:（59）Are you well prepared for it?
Alice:（60）See you tomorrow!
Sam:See you!
A.How about your presentation?
B.He needs it for tomorrow's presentation.
C．l think so.
D．Where are you heading?
E．You are welcome.
F．No problem!
G．What can I do for you?
H．No，thanks!
第（59）题选
Alice:Hi,Sam!It's nice to see you here.
Sam:Hi,Alice!
Alice:（56）
Sam:To my dorm.
Alice:Great!Could you take this book to Peter?
Sam:（57）Does Peter know what it is for?
Alice:Yes.（58）
Sam:（59）Are you well prepared for it?
Alice:（60）See you tomorrow!
Sam:See you!
A.How about your presentation?
B.He needs it for tomorrow's presentation.
C．l think so.
D．Where are you heading?
E．You are welcome.
F．No problem!
G．What can I do for you?
H．No，thanks!
第（58）题选
Alice:Hi,Sam!It's nice to see you here.
Sam:Hi,Alice!
Alice:（56）
Sam:To my dorm.
Alice:Great!Could you take this book to Peter?
Sam:（57）Does Peter know what it is for?
Alice:Yes.（58）
Sam:（59）Are you well prepared for it?
Alice:（60）See you tomorrow!
Sam:See you!
A.How about your presentation?
B.He needs it for tomorrow's presentation.
C．l think so.
D．Where are you heading?
E．You are welcome.
F．No problem!
G．What can I do for you?
H．No，thanks!
第（57）题选
Alice:Hi,Sam!It's nice to see you here.
Sam:Hi,Alice!
Alice:（56）
Sam:To my dorm.
Alice:Great!Could you take this book to Peter?
Sam:（57）Does Peter know what it is for?
Alice:Yes.（58）
Sam:（59）Are you well prepared for it?
Alice:（60）See you tomorrow!
Sam:See you!
A.How about your presentation?
B.He needs it for tomorrow's presentation.
C．l think so.
D．Where are you heading?
E．You are welcome.
F．No problem!
G．What can I do for you?
H．No，thanks!
第（56）题选
There are many interesting news items in BP’s（英国石油公司）annual Energy Outlook just published.
But perhaps the most astonishing suggestion in the report is the idea that cutting back on plastic use could make matters worse.This might be what you would expect BP to say.After all，as one of the world's biggest oil companies，it makes a lot of money from selling products in plastic.But let's look at the thinking behind BP's argument.
If the current opposing idea about the use of plastic continues，there could be a worldwide ban on single-use plastics by 2040.But the document argues that switching plastic for other materials will have a bigger cost in terms of energy and carbon emissions（排放）.That sounds like the law of unintended（非故意的）consequences in action.When plastic bags are measured against paper or cotton substitutes，a BBC analysis found there wasn't a great deal of difference in their environmental impact.Paper bags require fewer reuses to make them more environmentally friendly than single-use plastic bags，which means customers have to replace paper bags more frequently.
Environmentalists，though，are not entirely convinced.They think that BP is stressing the problem of banning plastic for its own interest.“While it's true that it takes less energy to produce and transport plastic than glass，a glass bottle can be reused dozens of times and is recyclable.Plus，materials like glass when they escape collection don't go on polluting our oceans and rivers for hundreds of years，"said Louise Edge，from Greenpeace UK.
Steps to encourage recycling are being taken.The UK，for example，will introduce a new tax on the manufacture and import of plastic packaging in 2022.
There are also lots of developments taking place with alternative materials.These may be the final defense against the unintended consequences of plastic bans.
What measure is being taken by the UK to cut back on the use of plastics?
There are many interesting news items in BP’s（英国石油公司）annual Energy Outlook just published.
But perhaps the most astonishing suggestion in the report is the idea that cutting back on plastic use could make matters worse.This might be what you would expect BP to say.After all，as one of the world's biggest oil companies，it makes a lot of money from selling products in plastic.But let's look at the thinking behind BP's argument.
If the current opposing idea about the use of plastic continues，there could be a worldwide ban on single-use plastics by 2040.But the document argues that switching plastic for other materials will have a bigger cost in terms of energy and carbon emissions（排放）.That sounds like the law of unintended（非故意的）consequences in action.When plastic bags are measured against paper or cotton substitutes，a BBC analysis found there wasn't a great deal of difference in their environmental impact.Paper bags require fewer reuses to make them more environmentally friendly than single-use plastic bags，which means customers have to replace paper bags more frequently.
Environmentalists，though，are not entirely convinced.They think that BP is stressing the problem of banning plastic for its own interest.“While it's true that it takes less energy to produce and transport plastic than glass，a glass bottle can be reused dozens of times and is recyclable.Plus，materials like glass when they escape collection don't go on polluting our oceans and rivers for hundreds of years，"said Louise Edge，from Greenpeace UK.
Steps to encourage recycling are being taken.The UK，for example，will introduce a new tax on the manufacture and import of plastic packaging in 2022.
There are also lots of developments taking place with alternative materials.These may be the final defense against the unintended consequences of plastic bans.
According to environmentalists，what causes BP to oppose banning plastics?
There are many interesting news items in BP’s（英国石油公司）annual Energy Outlook just published.
But perhaps the most astonishing suggestion in the report is the idea that cutting back on plastic use could make matters worse.This might be what you would expect BP to say.After all，as one of the world's biggest oil companies，it makes a lot of money from selling products in plastic.But let's look at the thinking behind BP's argument.
If the current opposing idea about the use of plastic continues，there could be a worldwide ban on single-use plastics by 2040.But the document argues that switching plastic for other materials will have a bigger cost in terms of energy and carbon emissions（排放）.That sounds like the law of unintended（非故意的）consequences in action.When plastic bags are measured against paper or cotton substitutes，a BBC analysis found there wasn't a great deal of difference in their environmental impact.Paper bags require fewer reuses to make them more environmentally friendly than single-use plastic bags，which means customers have to replace paper bags more frequently.
Environmentalists，though，are not entirely convinced.They think that BP is stressing the problem of banning plastic for its own interest.“While it's true that it takes less energy to produce and transport plastic than glass，a glass bottle can be reused dozens of times and is recyclable.Plus，materials like glass when they escape collection don't go on polluting our oceans and rivers for hundreds of years，"said Louise Edge，from Greenpeace UK.
Steps to encourage recycling are being taken.The UK，for example，will introduce a new tax on the manufacture and import of plastic packaging in 2022.
There are also lots of developments taking place with alternative materials.These may be the final defense against the unintended consequences of plastic bans.
Which of the following could be banned worldwide by 2040?
There are many interesting news items in BP’s（英国石油公司）annual Energy Outlook just published.
But perhaps the most astonishing suggestion in the report is the idea that cutting back on plastic use could make matters worse.This might be what you would expect BP to say.After all，as one of the world's biggest oil companies，it makes a lot of money from selling products in plastic.But let's look at the thinking behind BP's argument.
If the current opposing idea about the use of plastic continues，there could be a worldwide ban on single-use plastics by 2040.But the document argues that switching plastic for other materials will have a bigger cost in terms of energy and carbon emissions（排放）.That sounds like the law of unintended（非故意的）consequences in action.When plastic bags are measured against paper or cotton substitutes，a BBC analysis found there wasn't a great deal of difference in their environmental impact.Paper bags require fewer reuses to make them more environmentally friendly than single-use plastic bags，which means customers have to replace paper bags more frequently.
Environmentalists，though，are not entirely convinced.They think that BP is stressing the problem of banning plastic for its own interest.“While it's true that it takes less energy to produce and transport plastic than glass，a glass bottle can be reused dozens of times and is recyclable.Plus，materials like glass when they escape collection don't go on polluting our oceans and rivers for hundreds of years，"said Louise Edge，from Greenpeace UK.
Steps to encourage recycling are being taken.The UK，for example，will introduce a new tax on the manufacture and import of plastic packaging in 2022.
There are also lots of developments taking place with alternative materials.These may be the final defense against the unintended consequences of plastic bans.
What is astonishing about BP's annual report?
Vegans try to live，as much as possible，in a way that avoids exploiting and being cruel to animals.This means following a plant-based diet.Vegans do not eat animals or animal-based products like meat，fish，seafood，eggs，honey and dairy products such as cheese.For many vegans，living a committed vegan lifestyle means not wearing clothes made from animal skin sand avoiding any products which have been tested on animals.
Vegans argue that suffering is caused in the production of these foods.For example，they say that，on some dairy farms，male calves（小牛）are killed because they are too expensive to keep，and cows are killed when they get older and produce less milk.As for honey，vegans say that bees make honey for bee，not for humans，and that bees’health can suffer when humans take the honey from them.Vegans believe that the products they use and consume should be free from not just cruelty but any exploitation of animals.
The main reason for going vegan is probably that they believe
animals and all other sentient（有感知能力的）beings should have the
right to life and freedom.However，there are other reasons.Vegans
argue that the production of meat and other animal products is very bad
for the environment.They point out that a huge quantity of water is
needed to grow grain to feed animals in the meat industry.The
enormous amount of grain which the meat industry needs often leads to
forests being cut down and habitats（栖息地）being lost.In contrast，
much lower quantities of grain and water are needed to sustain a vegan
diet.In addition，many vegans say that all the nutritious elements our
bodies need are contained in a carefully planned vegan diet and that this
type of diet helps prevent some diseases.
What does the author want to imply in this passage?
