问题描述：
He ________for three year.
1.He ________for three year.
A.has joined the army B.has been in the amy c.joined the army D.has joined in the army
2.There is no air _____water on the moon.
A,and B.or C.so D.yet
（1的答案是B,为什么吖?为什么不是A呢?）
（2的答案是B,为什么吖?这不是否定句吖,只有There isn't才要用or ）
1.He ________for three year.
A.has joined the army B.has been in the amy c.joined the army D.has joined in the army
2.There is no air _____water on the moon.
A,and B.or C.so D.yet
（1的答案是B,为什么吖?为什么不是A呢?）
（2的答案是B,为什么吖?这不是否定句吖,只有There isn't才要用or ）
问题解答：
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