What is the most important factor for a rocket to escape from the Earth? ______ When a bicycle "coasts" downhill, it ______.

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问题 What is the most important factor for a rocket to escape from the Earth? ______
When a bicycle "coasts" downhill, it ______.

选项 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

答案B

解析 从第三段最后一句“自由落体并不意味着火箭会朝地球落下来,而是不需要外力的帮助在太空中自由飞行,就像沿山坡滑行的自行车一样”,可以判断本题的答案是B。
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