GWD24-1 era 可以和during相接吗?

RedEye

 

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.

    

1. an era when the city had transformed.
2. An era during which the city was transformed.
3. An era that transformed it.
4. During which era the city transformed.
5. During which the city was transformed.             The answer is B. However, I think that era means a period of time so it is not right to follow by during. Therefore, the best answer should be E. Any comments?

micyuanfei

E肯定不对。which没有指代对象。

era是a period of history or a long period of time，而既然有period，就肯定可以用during（在一段时间——period——之间）

huanglingzi

仍然不是很明白，难道E中的which不能指代1973-1993么？