◎ 题干
At present, the ____ are too slow to carry many people to Mars.  
[     ]
A. space shuttle  
B. spacecrafts  
C. spacecraft  
D. underground
◎ 答案
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“At present, the ____ are too slow to carry many people to Mars. [ ]A. space shuttle B. spacecraftsC. spacecraftD. underground…”主要考查了你对  【可数名词(单数名词,复数名词)】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。