When you are sleeping, you had better _____ all your windows closed. [ ]

How can I make full use of my time? —Makea clear timetable first．

Can you tell us ________?— Of course, but they’re coming over to visit me in a few months.

There will be ________water and ________trees in 100 years, how can we live?

Susan thought ____not easy to answer all these questions.