问题补充：
-----They used to be good friends, but now they are like strangers. ----- How this ?
A. were; come about
B. did; come about
C. were; taken place
D. were; happened
答案：
A. were; come about
(答案→)B. did; come about
C. were; taken place
D. were; happened
解析： come about, take place, happen都是发生的意思，均无被动语态。
