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
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
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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