Can animals be made to work for us?Some scientists think that one day animals may be trained?to do a number of simple jobs that are now done by human beings.
They point out that at a circus,for example,we may see elephants,monkeys,dogs and other ani-mals doing quite skillful things.Perhaps you have seen them on the television or in a film.If you?watch closely,you may notice that the trainer always gives the animal a piece of candy or a piece of?fruit as a reward.The scientists say that many different animals may be trained to do a number of?simple jobs if they know they will get a reward for doing them.
Of course,as we know,dogs can be used to guard a house,and soldiers in both old and modern?times have used geese to give warning by making a lot of noise when a stranger or an enemy comes?near.But it may be possible to train animals to work in factories.In Russia,for example,pigeons?which are birds with good eyesight,are being nsed to watch out for faults in small steel balls that are?being made in one factory.When the pigeon sees a ball which looks different from others,it touches a?steel plate with its beak.This turns on a light to warn people in the factory.At the same time a few?seeds are given as a reward.It takes three to five weeks to train a pigeon to do this and one pigeon?can inspect 3,000 to 4,000 balls an hour.
Apes have been used in America in helping to make cars,and scientists believe that these large?monkeys may be one day gather crops and even drive trains.
Many animals may be trained to do simple jobs if they know__________.
由第二段最后一句“The scientists say that?many different animals may be trained to do a number of?simple jobs if they know they will get a reward for doing?them．”可知C项正确。
把10gMgCl2和MgSO4的混合物溶于适量水中，滴加2mol／L的BaCl2溶液至沉淀完全，共消耗BaCl2溶液25mL。求混合物中MgCl2和MgSO4的质量各是多少克
固定在匀强磁场中的正方形导线框abcd，各边长为1．其中ab是一段电阻为R的均匀电阻丝，其余3边均为电阻可忽略的铜线。磁场的磁感应强度为B，方向垂直纸面向里。现有一与ab段的材料、粗细、长度都相同的电阻丝PQ架在导体框上，如图所示。PQ以恒定速度方向如何
一小物块以速度v0=10m／s沿光滑地面滑行，然后沿光滑曲面上升到顶部水平的高台上，并由高台上飞出，如图所示。问当高台的高度h多大时，小物块飞行的水平距离最大这个距离是多少(g=10m／s2)
某晶体盐的水溶液呈浅绿色，在此溶液中通入氯气，溶液变为棕黄色，把所得棕黄色溶液分成两份：一份加入KSCN溶液，溶液变深红色；另一份加入BaCl2溶液，产生不溶于稀HNO3的白色沉淀，则该晶体盐的化学式是_______。
欲除去乙烷中的乙烯，可将混合气体通过盛有_______的洗气瓶；欲除去乙炔中的硫化氢，可将混合气体通过盛有_______的洗气瓶。
浓硝酸常盛装在棕色瓶中，且贮放在冷暗处，原因是_______，
碳酸氢钠溶液和烧碱溶液反应的离子方程式为_______。
常温下，氨水中存在的离子有_______。
在酸或碱存在的条件下，甲酸甲酯跟水发生水解反应的化学方程式为_______。
有下列几种气体：H2、O2、HCl、NO、NH3、CH4，其中通常情况下能用来和水做“喷泉”实验的是_______。
