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