—Mary, could you tell me if your mother ________ our school sports meeting tomorrow?　　—I think she will come to school if she _________ free.　　

—Is this room   _____  ?     —Yes, it’s theirs.

I don’t know how ________ commas. 

--- Mr. Wang’s never been to Canada, has he?---           . He went there on business last week.

--Laura didn’t join in their dancing last night , did she ?---________________, because she fell off her bike and hurt her legs