读“干洁空气的主要成分（25千米以下）”表，回答1～3题。
小题1:干洁空气中体积比例最大的是
A．氮（N2）
B．氧（O2）
C．氩（Ar）
D．二氧化碳（CO2）小题2:对地面起到保温作用的是
A．氮（N2）
B．氧（O2）
C．氩（Ar）
D．二氧化碳（CO2）小题3:低层大气中除干洁空气外，主要还有
A．臭氧（O3）
B．氨气（NH3）
C．甲烷（CH4）
D．水汽和杂质
小题1:A
小题2:D
小题3:D
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| My uncle is a farmer. He has ninety 1 trees on his farm. My uncle and my aunt 2 pick (采摘) all the apples in fall(秋天), 3 they ask my parents and me to go to 4 them every year. It's Sunday. My parents don't go to 5 and I don't go to school. So we'll go to the 6 . We get up early (早) in the 7 . My mother is in her 8 clothes. My father gets many kinds of food for my uncle's 9 in a shop. She likes them very much. I think my uncle and aunt will 10 us many apples after that. I like to work on the farm. | ||||
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