Dad, I’ve finished my assignment— Good, _____ you play or watch TV, you mustn’t disturb me[ ]

Many things that were once considered useful and _____, for example, tobacco, is now thought harmful.

Which subject is _____, Chinese or maths—I think maths is.

This kind of software for English study _____ a lot of students who are weak in oral English.

I’m afraid I must be off now —_________