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

A. man did know　　　　 B. man knew

C. didn’t man know　　　 D. did man know

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

A.    man did know B. man knew      C.didnot man know     D. did man know

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

A. man did know       B. man knew         C. didn’t man know    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?

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

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