求教一道GWD 语法

Libbyyao

GWD-24-1
Tom Bradley was mayor of Los Angeles from 1973 to 1993, an era when the city had transformed from a collection of suburban neighborhoods to the second-largest city in the United States.
A.    an era when the city had transformed.
B.    an era during which the city was transformed.
C.    an era that transformed it.
D.    during which era the city transformed.
E.    during which the city was transformed.

答案是B，A 错在哪里啊？看了答案还是闹不明白。 选了A when 在这里不行吗？

iamyaoyao

这个应该是时态的问题吧，没有表示过去的过去的时间词语，所以应该用一般过去时

holacraig

应该是语态问题吧，city是被transform的。

Libbyyao

哦哦 恍然大悟 无关乎when原来
谢谢~~