Actors in a play have to know their parts（ ）.
A、
in heart
B、
by heart
C、
in mind
D、
on mind
【正确答案】：B
【题目解析】：
know/learn sth. by heart：用心记；keep... in mind：把...牢记在心中，选B。句意：剧中的演员必须牢记自己的角色。
Actors in a play have to know their parts（ ）.
Actors in a play have to know their parts（ ）.
in heart
by heart
in mind
on mind
know/learn sth. by heart：用心记；keep... in mind：把...牢记在心中，选B。句意：剧中的演员必须牢记自己的角色。