It’s important ________ the piano well.

Encourage your children to try new things, but try not to _____them too hard. [ ]

下列各句中，没有语病的一句是

Do you know where the headmaster is? I have something urgent.—Oh, he ______ have gone far, for the computer is still on in the office.[ ]

The little fat professor is very popular with his students because he is good at ________ different teaching methods to make his class lively and interesting. [ ]