请选择ABCD.p,N)K'a/R1u/SNot until the early years of the 19th century___ what heat is7@-E(j(C'|
A. man did know7@-E(j(C'|
B. man knew7@-E(j(C'|
C. didn't man know7@-E(j(C'|
D. did man know7@-E(j(C'|