Not until the early years of the 19th ce
问题:
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
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