单项选择题

What is the most important factor for a rocket to escape from the Earth

A．To travel as fast as it can.
B．To overcome the Earth gravity.
C．To get away from the air resistance.
D．To have strong power in its operation.
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单项选择题
As there is always the Earth's gravitational pull, people ______.
A．accept it without questioning it
B．never notice its presence
C．hardly think about how to use it
D．often try to escape from it
单项选择题
When a bicycle coasts downhill, it ______.
A．runs along the hillside
B．does not need any further power
C．runs freely to all directions
D．does not meet with air resistance
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