Scientists first became concerned about the ozone layer in the mid-1980s when a hole was discovered in the layer above Antarctica during the winter. The hole was caused by chemicals used in refrigerators and air conditioners. When these chemicals are sent out into the atmosphere, they produce gases that destroy the ozone.

　　Concern about the protective ozone layer rose more recently when data(数据) from satellites and ground stations showed that ozone levels were dropping over areas other than Antarctica. Low ozone levels were recorded in the spring and summer over the United States and over other populated areas in the world.

　　Although many countries have already begun stopping the use of ozone destroying chemicals, the new findings are expected to advance the timetable for a total ban(禁止) of the chemicals.

　　24. The scientists have observed the ozone layer ________.

　　A. since 1980 B. since last winter

　　C. for more than 20 years D. for about one year

　　25. The ozone layer in the atmosphere can ________.

　　A. do a lot of good to human beings in many ways.

　　B. protect humans from diseases caused by bad weather.

　　C. do a lot of harm to human beings in the summer-time.

　　D. protect humans from harmful levels of ultraviolet radiation.

　　26. Scientists first found that there was a hole in the ozone layer ________.

　　A. above Arctic during the winter in the mid-1980s

　　B. above Antarctica during the winter in the mid-1980s

　　C. over somewhere in the north of the equator in 1980

　　D. over the U.S.A in the summertime in the mid-1980s

　　27. The damage to the ozone layer was caused by ________.

　　A. the changeable weather

　　B. ozone-destroying chemicals

　　C. chemicals from refrigerators

　　D. chemicals from air conditioners

四、课文语法填空（共10小题；每小题1.5分，满分15分）

　　No one knows ___28__ (exact) how the earth began, as it ___29__ (happen) so long ago. However, according to a widely __30__ (accept) theory, the universe began with a "Big Bang" that threw matter in all ___31__ (direction). After that, atoms began to form and combine to create stars and other bodies.

　　For several billion years after the "Big Bang", the earth was still just a cloud of dust. What it was to become was uncertain until between 4.5 and 3.8 billion years ago when the dust settled into __32__ solid globe. The earth became so violent that it was not clear __33__ the shape would last or not. It exploded loudly with fire and rock. They were in time __34___ (produce) carbon, nitrogen, water vapour and other gases, which were to make the earth's atmosphere. ___35_ is even more important is that as the earth cooled down, water began to appear on its surface.

　　What many scientists believe is that the continued presence of water allowed the earth to dissolve __36__ (harm) gases and acids into the oceans and seas. This produced a chain reaction, which made __37__ possible for life to develop.

五、书面表达（满分25分）

假设你是李华，最近从报纸上得知2017年敦煌文博会"Silk Road (Dunhuang) International Cultural Expo" 将于9月举行，组委会现面向全社会招募志愿者，要求英语口语流利，了解丝路文化及国外习俗等。请给组委会写一份信申请该职位。

注意：1. 字数100字左右；

2. 可以适当增加细节，以使行文连贯；

3. 开头已经写好，不计入总词数；

4. 参考词汇：recruit v. 招聘。