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  3. What is the most important factor for a rocket to escape from the Earth? ______ Why is it not necessary to provide powered flig

What is the most important factor for a rocket to escape from the Earth? ______ Why is it not necessary to provide powered flig

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问题 What is the most important factor for a rocket to escape from the Earth? ______
Why is it not necessary to provide powered flight in space all the time? ______
选项 A、Few spacecrafts complete their flight operations.
B、The Earth’s gravity cannot be overcome.
C、No further power is needed after the escape speed is reached.
D、Free fall takes the place of the Earth’s gravity pull.
答案C
解析 从文章第三段第一句“一旦火箭达到了脱离地心引力的速度，就不再需要更多的能量”，可以判断出此题的答案应为C。
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