Rainforests are home to a rich variety of medicinal plants, food, birds and animals. Can you believe that a single bush（灌木丛）in the Amazon may have more species of ants than the whole of Britain! About 480 varieties of trees may be found in just one hectare of rainforest.
Rainforests are the lungs of the planet-storing vast quantities of carbon dioxide and producing a significant amount of the world's oxygen. Rainforests have their own perfect system for ensuring their own survival; the tall trees make a canopy（树冠层）of branches and leaves which protect themselves, smaller plants, and the forest animals from heavy rain, intense dry heat from the sun and strong winds.
Amazingly, the trees grow in such a way that their leaves and branches, although close together, never actually touch those of another tree. Scientists think this is the plants' way to prevent the spread of any tree diseases and make life more difficult for leaf-eating insects like caterpillars. To survive in the forest, animals must climb, jump or fly across the gaps. The ground floor of the forest is not all tangled leaves and bushes, like in films, but is actually fairly clear. It is where dead leaves turn into food for the trees and other forest life.
They are not called rainforests for nothing! Rainforests can generate 75%of their own rain. At least 80 inches of rain a year is normal-and in some areas there may be as much as 430 inches of rain annually. This is real rain-your umbrella may protect you in a shower, but it won't keep you dry if there is a full rainstorm. In just two hours, streams can rise ten to twenty feet. The humidity（湿气）of large rainforests contributes to the formation of rainclouds that may travel to other countries in need of rain.
12．What can we learn about rainforests from the first paragraph?
A．They produce oxygen. B．They cover a vast area.
C．They are well managed. D．They are rich in wildlife.
13．Which of the following contributes most to the survival of rainforests?
A．Heavy rains B．Big trees.
C．Small plants. D．Forest animals.
14．Why do the leaves and branches of different trees avoid touching each other?
A．For more sunlight. B．For more growing space.
C．For self-protection. D．For the detection of insects.
15．What can be a suitable title for the text?
A．Life-Giving Rainforests B．The Law of the Jungle
C．Animals in the Amazon D．Weather in Rainforests
12．D
13．B
14．C
15．A
【分析】
本文是说明文。热带雨林被称为“世界上最大的药房”，因为超过25%的现代药物是由其植物提炼。热带雨林也享有“地球之肺”的美誉，因其植物的光合作用净化地球空气的能力尤为强大。仅亚马逊热带雨林产生的氧气就占全球氧气总量的1/3。
12．细节理解题。根据第一段Rainforests are home to a rich variety of medicinal plants, food, birds and animals.得知，热带雨林蕴藏了丰富多彩的药用植物、食物以及鸟禽猛兽。可知，热带雨林有丰富的野生动物，故选D。
13．细节理解题。根据第二段Rainforests have their own perfect system for ensuring their own survival; the tall trees make a canopy（树冠层）of branches and leaves which protect themselves, smaller plants, and the forest animals from heavy rain, intense dry heat from the sun and strong winds.得知，热带雨林有自己完美的生存体系，高大的树木有枝干，树叶的树冠层保护树木本身、小植物、动物们免受大雨和太阳强风带来的干燥热浪的伤害。可知，大树有助于热带雨林生存，故选B。
14．推理判断题。根据第三段Scientists think this is the plants' way to prevent the spread of any tree diseases and make life more difficult for leaf-eating insects like caterpillars.得知，科学家们认为这是植物阻止任何树木疾病扩散和让比如毛毛虫这种食用树叶的昆虫难以生存。可以判断出不同树木的树叶和树枝避免彼此触碰是为了自我保护，故选C。
15．主旨大意题。本文首先讲述了热带雨林蕴藏了丰富多彩的药用植物、食物以及鸟禽猛兽。其次，热带雨林就是地球的肺——它吸纳了大量的二氧化碳，并制造了全球氧气的很大部分。然后，雨林可以自我形成所需降雨的75%，而庞大的热带雨林湿气则可以形成雨云，这些雨云则可以飘往那些缺雨水的国家。可以判断出本文最佳标题是“给予生命的热带雨林”，故选A。