单项选择题

Why computer data become imprecise in 1980s

A．The related programs on the computer were out of date.
B．More and more people drew water directly from the lake for drink.
C．A heavy rain happened around 1980.
D．The irrigation from the source water increases.

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单项选择题

What happened to the leaves falling from the trees in the second study

A．They broke down and the main parts turned into oxygen.
B．They broke down and the carbon content had mainly turned into carbon dioxide.
C．They broke down and the carbon content was mainly absorbed in the soil.
D．They absorbed more carbon dioxide.

单项选择题

The word it (Line 7, Para. 6) probably refers to ______.

A．carbon dioxide
B．nitrogen'
C．atmosphere
D．coal