Recent pressure at work may___ his behavior.

My grandfather is too old to care for himself, so my aunt is looking for someone to _____ him.

Peter must be ill.It's the only thing that can ________ his strange behavior.

   – Have they found out the _____ of the fire?--  Yes. It was a cigarette end that _____ the fire.

We must ______ the time that you’ve wasted this afternoon by working late to-night.