Not until the early years of the 19thcentury _____ what heat is.
A. Man did know
B. man know
C. didn’t man know
D. did man know
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If _______ , we will continue our experiment after office hours.
A. it be necessary
B. necessary
C. it being necessary
D. be necessary
Helen doesn’t like milk. But _________.
A. nor do I
B. so do I
C. neither I do
D. I do
It is by teaching ____ I make a living.
A. so
B. such
C. that
D. which
角膜组织中损伤后修复快且不留瘢痕的是( )
A. 上皮细胞层
B. 前弹力层
C. 基质层
D. 后弹力层
E. 内皮细胞层
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