Now Helen works _______ than before.
A:more carefully
B:more careful
C:much careful
D:much carefully
完全沉淀等物质的量浓度的NaCl、CaCl2和AlCl3三种溶液中的Cl-,消耗等物质的量浓度的AgNO3溶液的体积比为3:2:1,则三种氯化物溶液的体积之比为( )
“十月怀胎,一朝分娩”胎儿在母体内发育的场所是( )