-- _____ classes are there in your school? –Thirty.
Doctors advise us ________masks on such hazy days.
----Who _____the good idea at the meeting? ----Tom did.
---Tom, did you go to Sally’s party yesterday evening?----No, because I _________.
The foreigners find _____difficult to learn Chinese well.
Our English teacher is very popular among students because he always keeps his classes _____.