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

Not until the early years of the 19th century______ what heat is.

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

1. A.
   man did know
2. B.
   did man knew
3. C.
   didn't man know
4. D.
   did man know

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

A. man did know　　　　　　　　　 B. man know ?

C. didn’t man know 　　　　　　　 D did man know?