关于发电机和电动机，下列说法正确的是[ ]

A 、发电机把电能转化为机械能          

B 、电动机把机械能转化为电能

C 、发电机是根据电磁感应现象制成的    

D 、电动机是根据电磁感应现象制成的

A gas-free certificate would usually be issued by a (n)（）.

A.CCS marine surveyor

B.certified marine chemist

C.port engineer

D.HAS marine inspector