单项选择题

This passage is primarily about ______.

A．the greenhouse effect
B．the burning of fossil fuels
C．the potential effect of air pollution
D．the likelihood of a new ice age
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单项选择题
It is customary to leave a house
A．through the kitchen window
B．through a bedroom
C．by the door
D．down a drain-pipe
单项选择题
If the space animal theory is true, the creatures go down to the lower regions in order to ______.
A．escape detection
B．arouse curiosity
C．search for man-made energy
D．make contact with man
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