It？？s possible that all of the natural processes will be able to counterbalance anywarm-up or even reverse it.
On the other hand，computer models predict that a warm-up could go out ofcontrol. The problem is that we？？ve never experienced exactly what we are trying tofigure out. Only time can give the true answer.
So how do we measure global temperature？ We use averages of temperaturereadings throughout the many nations. This is not a complete picture because twothirdsof the world is covered by water. Satellites now carry sensors ( 传感器) thatgive us temperatures in remote locations.
As much as we understand about global warming，it？？s important to know that if awarm-up occurs，not all regions will get warmer. Some will get cloudier and wetter，while others cool down. Some regions may warm only at night while others are colderin one season and warmer in another . There are many possibilities and combinationsand the only certainty is that the Earth？？s temperature will change with time.
1. What does the word“ cloud”( para. 2) probably mean？
A. pollute B. affect C. devastate D. shroud
2. Which of the following can replace the word“ counterbalance”( para. 5) ？
A. detect the occurrence of B. defend
C. reduce the effect of D. apply
3. What does the writer want to tell us in paragraphs 5 and 6？
A. Global warming is a real threat to mankind.
B. There are disagreements on the possible consequences of global warming.
C. The actual effect of global warming might be less severe than we once thought.
D. Scientists are rather pessimistic about the problem of global warming.
4. Which of the following statements does the passage support？
A. The way to measure the global temperature has been improved.
B. Human activities alone can account for the greenhouse effect.
C. Reducing the emission of pollutants and gases will definitely stop the globalwarming.
D. If a warm-up takes place，it will get warmer all around the world.
( 2)
Acid rain，which is a form of air pollution，currently becomes a object of greatdebate because of widespread environmental damage for which it has been blamed. Itforms when oxides of sulfur ( 硫) and nitrogen ( 氮) combine with atmosphericmoisture to yield sulfuric and nitric acids，which may then be carried long distancesfrom their source before they drop in the form of rain. The pollution may also take theform of snow or fog or fall down in dry forms. In fact，although the term“ acid rain”has been in use for more than a century - it is derived from atmospheric studies thatwere made in the region of Manchester ，England - the more accurate scientific termwould be“ acid deposition ”. The dry form of such deposition is just as damaging tothe environment as the liquid form.
The problem of acid rain originated with the Industrial Revolution，and it hasbeen growing ever since. The severity of its effects has long been recognized in localsetting，as exemplified by the spells of acid smog in heavily industrialized areas. Thewidespread destructiveness of acid rain，however ，has become evident only in recentdecades. One large area that has been studied extensively is northern Europe，whereacid rain has eroded structures，injured crops and forests，and threatened life infreshwater lakes. In 1984，for example，environmental reports indicated that almosthalf of the trees in Germany？？s Black Forest had been damaged by acid rain. Thenortheastern United States and eastern Canada have also been particularly affected bythis form of pollution； damage has also been detected in other areas of these countriesand other regions of the world.
