According to this passage, which is the best title

A．How to become an ordinary teacher.
B．What a good teacher should do.
C．What teachers and actors could learn from each other.
D．The similarities and differences between a teacher' s work and an actor' s.

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