根据下面资料，回答43-46题
A world like no other—perhaps this is the best way to describe the world of the rainforest. No rainforest is the same—yet most rainforests can be found in the small land area 22.5 degrees north and 22.5 degrees south of the Equator (赤道). You can find rainforests in South America and Indo-nesia. Other rainforests exist further from the Equator, in Thailand and Sri Lanka.
Rainforests have a great role to play in supporting the world. They are home to a rich variety of plants, birds and animals. Can you believe that 480 varieties of trees may be found in just one hec-tare (公顷) of rainforest These forests have around 50% of all the plants, birds and animals on Earth.
Rainforests have their own perfect way for living. The tall trees make a huge umbrella of bran-ehes and leaves which protect themselves, smaller plants, and the forest animals from heavy rain, dry heat from the sun and strong winds. Rainforest trees grow in such a way that their leaves and branches, although close together, never actually touch those of another tree. Scientists think this isa way to prevent the spread of any tree diseases and make life more difficult for leaf-eating insects(昆虫). To live in the forest, animals must climb, jump, or fly across the branches and trees. The ground floor of the forest is not all leaves and bushes, like in films, but is actually fairly clear. It is where leaves become food for the trees and other forest life.
Rainforests around the world are disappearing at a high speed. A few thousand years ago, rain-forests covered as much as 12% of the land surface on Earth, but today this has fallen to less than5.3%. We hope that the world governments work together with scientists to use their power and knowledge to keep the rainforests for our existence.
Why are rainforests important to the world
事实细节题。根据第二段前两句可知，热带雨林在维持世界生态平衡方面有巨大作用，它们是众多动植物的家园。故本题选C。
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_______。
