Teachers’ job is ______ the students learn well.
| A．helping | B．help | C．to help | D．helped |
According to the new family planning policy in China, a couple can have a_______child if one of them is an only child.
A. two B. second C. twice
Look at the sign _______! We shouldn't park our car here.
The telephone rang_______ Jenny was practicing the violin.
A. until B. before C. while
--- Hi, David. _______do you go to see your grandparents?
---About three times a month.
A. How long
B. How often
C. How soon
The year of 2013 saw the_______ air pollution in China for 52 years.
A. bad B. worse C. worst