-_______students are there in your class, Mr Li?  -Fifty. 

Pip’s sister seldom has a kind word to say, ＿＿ she?

— _______ are they doing?一They are running．

I think that something has to be done to stop the air from being polluted, ______ ?

I told mom that not everyone could manage to have 3 meals on time everyday, _____?