100L空气中含有二氧化碳约      L，稀有气体约        L。

Directions.

A. Study the following picture carefully and write an essay in no less than 160-200 words.

B. Your essay must be written clearly on ANSWER SHEET 2.

C. Your essay should meet the requirements below:

1) Interpret the following picture,

2) analyze possible reasons for this situation, and

3) suggest counter-measures.