单项选择题

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

A．carbon dioxide
B．nitrogen'
C．atmosphere
D．coal
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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 dioxide.
单项选择题
Scientist Ram Oren is of the opinion that common beliefs of the tree's ability to absorb carbon dioxide are ______.
A．biased
B．insightful
C．overoptimistic
D．totally wrong
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