问题
选择题
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
答案
答案:D
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
答案:D