（）to use crutches for six months severely limited Mr. Locke's ability to work in the shipping facility.

单项选择题The policeman asked the boy （）

A. where is his mother
B. where his mother is
C. where was his mother
D. where his mother was

单项选择题The secretary tried to （） the smoke by opening a window of the meeting room.

A. deface
B. detect
C. discriminate
D. dissipate

单项选择题All children are avid （） praise.

A. on
B. for
C. with
D. at

单项选择题—When （）you（）to learn to skate —Five years ago.

A. do; start
B. will; start
C. had; started
D. did; start

单项选择题—Thanks for your help. —（）

A. No, thanks
B. Let me see
C. It doesn't matter
D. That's OK