Some people haven’t realized something as common as _______to the sun for a long time will do harm to their skin and even cause skin cancer.

The computer center, ________ last year, is very popular among the students in this school.

I walked out of the cinema, ______ to return to see the wonderful film next Sunday. 

The bell __ the end of the period rang, __our heated discussion.

________ some more chairs，tables and so on, the room looked more beautiful.