Last night Mr Crook didn’t come back at the usual time______，he met some friends and stayed out until midnight

Dad, why must I stop______ computer games — For your health , my boy.

The Math problem is too difficult , we really don’t know ________ to do it .

I’m fond of my sister, but she has a serious shortcoming. She _______ be really stubborn.

I don’t know _____ tomorrow. Can you tellme?