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问题
选择题
The teacher said that doubt ____ the key of knowledge.
A. were
B. are
C. was
D. is
答案
答案:
D
单项选择题
胎儿纵轴与母体纵轴垂直
A.羊水过多
B.过期妊娠
C.胎儿窘迫
D.协调性宫缩乏力
E.不协调性宫缩乏力
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单项选择题
机械效率等于在克服机械损失后剩余功率与功率的()
A、之积
B、之和
C、比值
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