You’d better ________late next time .

We may never discover what _____ that night when you left for Beijing.[ ]

I think it’s not in the length of days, but in the use we make of them_____ the value of life lies.

There is ________“s” and ________“f”in the word “useful” .

It was __________ computer games thatcost the young man a lot of precious time that he ought __________ on hislessons．