Question

Not until the early years of the 19th century _________．

1. A.
   man did know heat is what
2. B.
   man know what is heat
3. C.
   did man know what heat is
4. D.
   didn’t man know heat

Answer 1

C
本句考查倒装结构，否定词not置于句首强调状语时主句需要倒装，故C项正确。