Not until the early years of the 19th century what heat was.A. man did knowB. did man kne

问题补充：

Not until the early years of the 19th century what heat was.

A. man did know

B. did man knew

C. didn man know

D. did man know

答案：

A. man did know

B. did man knew

C. didn man know

D. did man know

解析：考察倒装句。Not until的句式放在句首时，后面的主句使用部分倒装的形式。故D正确。