Tom Bradley was mayor of Los Angeles

[BTGmoderatorDC]

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

Why Option C isn't the best Option?

OA B

[DavidG@VeritasPrep]

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

Why Option C isn't the best Option?

OA B

C has a logic problem - this option makes it sound as though "the era" were an active agent that changed Los Angeles, as opposed to the time frame in which the change occurred.