单句语法填空
1．More attention should be paid to (improve) the safety of school buses, which has become a big concern of the whole society.
答案：improving
2．Around 540 million people (affect) by secondhand smoke, which causes 100, 000 deaths per year.
答案：are affected
3．I received a letter (contain) some important information about the project.
答案：containing
4．I got close enough to hear them speaking Chinese, and I said “Ni Hao”， just I might do in China.
答案：as
5．So I suggest you (keep) the balance between your study and entertainment, such as doing sports, listening to music and so on.
答案：(should) keep
