She makes it a rule to ______ aside an hour each day for learning new vocabulary.

A．A teacher has to learn by heart what exactly he is going to say in class.
B．A teacher can not decide beforehand what exactly he is going to say in class.
C．A teacher’s voice must be nicer than an actors.
D．A teacher must have a better memory than an actor.

A．do we should
B．should we
C．we should
D．we do should