Why was he unhappy yesterday? —A letter from home ______ an attack of homesickness.

Could you give us some advice about this competition?—If you want to win first prize,your design for the museum must be________.[ ]

Who’s ___________ friend—His friend is Mike.

It is advised by health experts that windows should be opened now and then for air to _____, whichmakes the air in your room fresher. [ ]

I’ve become good friends with several of the students in my school________I met in the English speech contest last year.