单项选择题

Not until the early years of the 19th century（）what heat is.

A．man knew
B．did man know
C．man did know
D．didn't man knew

相关考题

After searching for half an hour, she realized that her...

单项选择题After searching for half an hour, she realized that her glasses（）on the table all the time.

A．had been lain
B．have been lying
C．were lain
D．had been lying