(  )40. I was doing my homework          the door bell rang.

A. when         B. while               C. after             D. before

(  )41. Do you know         ?

A. what he happened                     B. what did he happened

C. what happened to him                  D. what the matter is with him

(  )42. Without proper lessons, you could         a lot of bad habits when playing the piano.

A. give up       B. catch up             C. pick up           D. keep up

(  )43. Do you have trouble          the foreigners?

A. understanding  B. to understand         C. understand        D. understood

(  )44. I was          to see the police at my home yesterday.

A. amazing       B. surprising            C. surprised         D. interesting

(  )45. Do you know          at this time yesterday?

A. what she is doing                      B. what is she doing

C. what was she doing                    D. what she was doing