问题
选择题
Not until the early years of the 19th century ________ what heat was. [ ]
A. man did know
B. did man knew
C. didn't man know
D. did man know
答案
答案：D
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Not until the early years of the 19th century ________ what heat was. [ ]
A. man did know
B. did man knew
C. didn't man know
D. did man know
答案：D