GWD-24-1 对答案质疑

请问这题应该选B还是E啊？

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.

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.

Answer:

我是选B的

但是刚才看到论坛之前一个牛人的在另一题的例子~~

OG-220 For almost a hundred years after having its beginning in 1788, England exiled some 160,000 criminals to Australia.
            

(D)
                During a hundred years, a period beginning in 1788,

(E)  Over a period of a hundred years beginning in 1788, 对。
            

OG对D的解释：Choice D is awkward and unidiomatic, and nonsensically suggests that a hundred years is defined as a period beginning in 1788. Precise and idiomatically phrased, choice E is best.
            

又觉得好像应该选E

但是这题的E和og的E有点不一样~~

og的E a period of a hundred years 这里却没有 an era from 1973 to 1993

应该选哪个？？？

B is the answer I think

E make "which" had nothing to refer

for B