(2017·北京) Jim has retired, but he still remembers the happy time ________ with his students.
A. to spend B. spend
C. spending D. spent

(2017·北京卷·单项填空)—Peter, please send us postcards ________ we'll know where you have visited.
—No problem.

A．but	B．or
C．for	D．so

______ birds use their feathers for flight, some of their feathers are for other purposes.

A．Once

B．If

C．Although

D．Because

—________ that company to see how they think of our product yesterday?
—Yes. They are happy with it.
A. Did you call   B. Have you called
C. Will you call   D. Were you calling

If the new safety system _______ to use, the accident would never have happened.
A. had been put B. were put C. should be put D. would be put

(2017·北京卷·单项填空）The little problems ________ we meet in our daily lives may be inspirations for great inventions.

A．that	B．as
C．where	D．when

(2017·北京) Jane moved aimlessly down the tree-lined street, not knowing ______she was heading.

A．why	B．where
C．how	D．when