单项选择题

The scientists are not sure______.

A．how long the ice age lasted
B．where ice sheets (冰川) melted during the ice age
C．what caused the temperature changes
D．what the earth is made up of
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单项选择题
The North Pole is surrounded by land, while the South Pole is surrounded by the Antarctic Ocean. So scientists thought that______.
A．most of the ice melted in the Northern hemisphere
B．most of the ice melted in the Southern hemisphere
C．The North Pole is colder than the South Pole
D．The South Pole is colder than the North Pole
单项选择题
Only one of these pairs of glasses is worth______.
A．to be gought
B．being bought
C．bought
D．buying
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