I don’t know why ___________.

A. my sister Mary was laughing

B. did my sister Mary laugh

C. my sister Mary laughing

D.was my sister Mary laughing

Tom's work at school is above the __________ . (平均)

The open-air celebration has been put off _______ the bad weather.

A. in case of　　　　　 B. in spite of　　　　　　　 C. instead of　　　　　 D. because of

Neither side was willing to give in at all. As a result, no agreement ___________.

A. was reached　 B. has reached

C. had reached　 D. had been reached

She doesn’t have a natural talent but she ________ for it with hard work.

A. puts up　　 B. makes up　　　 C. stays up　　　 D. takes up

It was _____ computer games that cost the boy a lot of time that he ought to have spent on his lessons.

A. to have played            B. playing　　     C. played                    D. having played

----How are you doing?

　 ----Why? I ______ you _____ not coming.

A. think; are　 B. thought; were　 C. think; were　 D. thought; are

—Someone is knocking at the door. _____ it be Venis?

   —No, it _____ be her; she left for New York this morning.

   A. Can; mustn’t     B. Might; can’t   　 C. May; doesn’t     D. Can; can’t

The bus rolled into the valley, _______ over 20 deaths.

A. caused       B. having caused        C. causing    D. to cause

The cells are so __________that we can’t see them with our eyes.