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很久以前人们就开始梦想宇宙之旅。这种旅行由于火箭的发明而与现实拉近了距离，现在人们可以乘坐载人飞行火箭，到月亮上去，也可以探测宇宙。火箭可以飞向宇宙是因为有牛顿的“第三定律”，即作
Long ago people began to dream about the journey to the universe. The trip was brought closer to reality as a result of the rocket invention, and now people can take the manned flying rocket to the moon and the universe. Rockets can fly to the universe because of Newton’s “third law,” that is