Why is it not necessary to provide powered flight in space all the time？
A. Few spacecrafts complete their flight operations.
B. The Earth's gravity cannot be overcome.
C. No future power is needed after the escape speed is reached.
D. Free fall takes the place of the Earth's gravity pull.
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It can be inferred from the passage that glaciers were primarily made up of seawater.
A. Right
B. Wrong
C. Not mentioned
Why had they left England？
A. Because of religious problem.
B. To set up a new religion.
C. To learn new farming.
D. Because of the Indians.
According to the passage, before the Ice Age the continental shelf was submerged in water.
A. Right
B. Wrong
C. Not mentioned
As there is always the Earth's gravitational(地心引力的)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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