In some countries,students have to wear ______ uniform to school.
A) a B) an C) the D) /
The Smiths_______in this housing estate,didn't they?
A) used to living B) used to live C) are used to live D) are used to living
You should apologize to Mr.Li__________you know you did something wrong.
A) whenerver B) since C) until D)unless