单项选择题

How fast will a rocket go to escape completely from the Earth's gravity ______

A．Seventy miles per second.
B．Seven thousand miles per hour.
C．Twenty-five thousand miles per second.
D．Twenty-five thousand miles per hour.
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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.
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
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