2. 外语
  3. The passage is mainly about ______. The major difficulty in developing space travel is that ______.

The passage is mainly about ______. The major difficulty in developing space travel is that ______.

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问题 The passage is mainly about ______.
The major difficulty in developing space travel is that ______.
选项 A、there is no clear destination in space
B、it is too risky and expensive for people to go beyond the orbit
C、the current space propulsion systems can not meet the needs for the long space travel
D、there is not enough energy for spacecraft to gain velocity
答案C
解析 细节题。根据第二段第三句“当今的空间推进技术做了努力，把探测仪送往太阳系的远端。”可知C“目前飞船推进系统无法满足长距离太空旅行的需要”是发展太空旅行的主要困难。
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大学英语六级

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