In the middle of winter, when snow is falling in many parts of the United States, scientists have sounded a warning to people who plan to spend many hours in the sun this summer．The warning is：The sun's summertime rays(射线)are more dangerous than once thought． 　　A team of scientists from 80 nations recently reported to the United Nations that a layer of ozone(臭氧层)in the atmosphere(大气)，which protects humans from harmful levels of ultraviolet(紫外线)radiation(放射)，will be thinner over the United States this summer．The thinner layer allows more ultraviolet rays from the sun to reach the earth．The extra amount of ultraviolet radiation could cause an increase in the number of cases of skin cancer(癌症)． 　　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(冰箱)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． (1) The scientists have observed the ozone layer ________． [　　] A． since 1980 B． since last winter C． for about 20 years D． for about one year (2) The ozone layer in the atmosphere can ________． [　　] A． do a lot of good to human beings in many ways B． protect human beings from disease caused by bad weather C． do a lot of harm to human beings in the summertime D． protect human beings from harmful levels of ultraviolet radiation (3) 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 (4) Which of the following is NOT true? [　　] A． The use of ozone destroying chemicals has already been stoppeD． B． The ozone levels in the spring and summer over the US were low． C． More and more people have begun to protect the nature surroundings． D． Many countries have already taken measures to protect the layer．

In the middle of winter, when snow is falling in many parts of the United States, scientists have sounded a warning to people who plan to spend many hours in the sun this summer．The warning is：The sun's summertime rays(射线)are more dangerous than once thought． 　　A team of scientists from 80 nations recently reported to the United Nations that a layer of ozone(臭氧层)in the atmosphere(大气)，which protects humans from harmful levels of ultraviolet(紫外线)radiation(放射)，will be thinner over the United States this summer．The thinner layer allows more ultraviolet rays from the sun to reach the earth．The extra amount of ultraviolet radiation could cause an increase in the number of cases of skin cancer(癌症)． 　　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(冰箱)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．
(1)	The scientists have observed the ozone layer ________． [　　] A． since 1980 B． since last winter C． for about 20 years D． for about one year
(2)	The ozone layer in the atmosphere can ________． [　　] A． do a lot of good to human beings in many ways B． protect human beings from disease caused by bad weather C． do a lot of harm to human beings in the summertime D． protect human beings from harmful levels of ultraviolet radiation
(3)	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
(4)	Which of the following is NOT true? [　　] A． The use of ozone destroying chemicals has already been stoppeD． B． The ozone levels in the spring and summer over the US were low． C． More and more people have begun to protect the nature surroundings． D． Many countries have already taken measures to protect the layer．