No one can walk the wire without a bit of fear unless ____very youngA having been trained B trained C to be trained D being trained 我选的A可是答案是B,为什么?这题考的是什么语法点?

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No one can walk the wire without a bit of fear unless ____very youngA having been trained B trained C to be trained D being trained 我选的A可是答案是B,为什么?这题考的是什么语法点?
No one can walk the wire without a bit of fear unless ____very young
A having been trained
B trained
C to be trained
D being trained
我选的A可是答案是B,为什么?这题考的是什么语法点?

No one can walk the wire without a bit of fear unless ____very youngA having been trained B trained C to be trained D being trained 我选的A可是答案是B,为什么?这题考的是什么语法点?
having been trained 既表进行又表完成,这里不需要进行时,没有强调过程,如果要选A 需要在后面加上一个since,表达自从很小就受过训练.
C意思完全不对.D 表达一直在被训练和后边的very young不符合.
trained过去分词,表示被动
故选B是对的,完整句子应该是unless( he or she) (is) trained( when) very yong.
考查的就是unless引导的条件从句省略了he is