By the time we started our work, he had explained everything clearly.
A.Before we had started our work, he explained everything clearly.
B.After we started our work, he had explained everything clearly.
C.We started our work before he had explained everything clearly.
D.After he had explained everything clearly, we started our work.

I did all my homework, and then I went out with my friends.
A.Before I did all my homework, I had gone out with my friends.
B.
C.Before I went out with my friends, I had done all my homework.
D.After I did all my homework, I went out with my friends.

Mr. Brown bought this car five years ago.
A.It has been five years when Mr. Brown has bought this car.
B.It is five years ago since Mr. Brown has bought this car.
C.Mr. Brown has had this car for five years .
D.Mr. Brown started to buy this car for five years.

Having finished their work, the workers expected to be paid.
A.The workers expected to be paid because they had finished their work.
B.Having expected to be paid, the workers finished their work.
C.Having their work finishing, the workers expected to be paid.
D.Having been finished their work, the workers expected to be paid.

Immediately after her arrival, it rained heavily.
A.No sooner had she arrived than it rained heavily.
B.As soon as she arrived, it rained heavily.
C.No sooner she had arrived than it rained heavily.
D.No sooner had she arrived when it rained heavily.

He was last in touch with me three weeks ago.
A.He hasn’t been in touch with me for three weeks.
B.He has been in touch with me for three weeks.
C.The last time he was in touch with me for three weeks.
D.It is three weeks ago since he was in touch with me.

When did you last ride a bike?
A.How many times have you ridden a bike?
B.How long is it since you last rode a bike?
C.How long did you ride a bike?
D.How long have you ridden a bike?

She has run (A) for (B) the past (C) two hours, and now she is exhausted (D).
A.the past (C)
B.exhausted (D)
C.has run (A)
D.for (B)

I started to study (A) Chinese since (B) I was (C) at the age of 15 (D).
A.started to study (A)
B.at the age of 15 (D)
C.since (B)
D.was (C)

When (A) my father was reading (B), my mother was mopping (C) the floor (D).
A.the floor (D)
B.was reading (B)
C.was mopping (C)
D.When (A)