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

Thank you for looking after my son while we were away.一

If water becomes increasingly scarce in decades _______, water shortage will become a hot issue all over the world.[ ]

you worked here since you graduated—No, I ____________at a factory in Beijing for sixyears.

Could you please help me with this problem?—Certainly. First of all, let’s __________ the problem and see what went wrong. [ ]