阅读短文，然后根据内容完成问题。

　　Dr Ray：Then you must thank trees for that, too．Trees are natural air conditioners．(A)他们吸掉空气中的废气，然后把氧气释放到空气中。How many people are there in your class, Judy?

　　Judy：Forty-six．

　　Dr Ray：Well, one and a half hectares of trees could produce enough oxygen to keep your whole class alive and healthy for a year．

　　Judy：That's wonderful．

　　Dr Ray：(B)Trees cool the air as well as clean it．(C)Three trees can do the job of 15 air conditioners running almost all day．

　　Judy：You certainly know a lot about trees, Doctor Ray．

　　Dr Ray：Thank you, Judy, but I don't, really．Scientists are only now beginning to understand them．(D)________, did you know that when insects attack a tree, it can warn its neighbours? The trees can then protect themselves by producing a chemical that makes their leaves taste nasty．And some trees can join their roots together underground, and pass food and water around．Trees are communicating with one another, but we don't know how．

　　Judy：Are trees in danger?

　　Dr Ray：In great danger．We cut down and burn millions every year but we replace hardly any of them．We are destroying our best fighters against pollution．

1．将(A)译成英语：________

2．将(B)部分转换成：Trees ________　________ cool the air ________　________ clean it．

3．将(C)部分翻译成汉语：________

4．在(D)处填上一个合适的词语：________

5．找出文中描写树对空气作用的两个词：________　________