单项选择题

Why do the 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A．The related programs on the computer were out of date.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 dioxid

单项选择题

What is the purpose of this passage

A．Introduce some new ideas about the relationship between trees and carbon dioxide.
B．Introduce recent condition of global industrial pollution.
C．Call on people to plant more trees to reduce greenhouse gases.
D．Point out that power companies should be responsible for the rising levels of carbon dioxid