阅读理解 Directions:Read the following pass

题目：

阅读理解

     Directions:Read the following passage.Fill in the numbered blanks by using the information

from the passage.

   Write NO MORE THAN THREE WORDS for each answer.

     The atmosphere is a gaseous envelope that surrounds the Earth. It is a collection of gases, vapor and particulates surrounding the Earth.

     The atmosphere is very important to life on this planet because, firstly, it acts as a system for cycling and recycling carbon, nitrogen, oxygen and hydrogen; living things transform these elements into sources of carbohydrates and proteins for nourishment(营养). Secondly, it protects us from invisible threats such as the harmful ultraviolet radiation from the sun. Thirdly, it protects the Earth's surface from rapid heating during the day and rapid cooling down at night. Lastly, it provides us with the air we breathe as it is our basic life support system; every breath we take requires oxygen in the air.

     However, human activities are causing the emission of harmful gases into the atmosphere. This has resulted in many environmental and health problems. Urban air pollution, acid rain, contamination by toxic chemicals, the lessening of the stratospheric ozone layer and changes in the global climatic system are all important environmental threats to the atmosphere.

     Air pollution

     Our planet is becoming choked with poisonous gases mostly from our daily activities like driving cars, warming out house and running power stations. And pollution doesn't need a passport to travel around the world.

     Ozone depletion

For years, chlorofluorocarbons(CFCs)were used as a cooling device in freezers and air conditioners. CFCs destroy the ozone layer, the layer that filters(过滤)ultraviolet radiation from the sun which causes eye damage and skin cancer.

     The greenhouse effect

     As more greenhouse gases released in the atmosphere reflect more heat back to the Earth, it causes a rise in temperature, beyond that which is considered to be normal. Rising temperature will cause the climate change, which may lead to more natural disasters, extinction(灭绝)of some animals and plants. Additionally, while passing through surface, some is lost in space. Greenhouse gases reflect back some solar energy and make the atmosphere hotter.

     Humans are damaging the atmosphere, which serves to be our coat. One day it deserves their right. And the world is warming up, the polar icecaps to melt, sea levels to rise and extreme weather conditions to occur more frequently.