SC難問？？＃2

When he had run for mayors of Cleveland in 1968, Carl strokes won the election, proving that an African American candidate can be elected in a city in which African Americans constitutes a minority of the population.

a)When he had run for mayors of Cleveland in 1968,
b)He ran for mayor of Cleveland in 1968, and
c)Running, in 1968, for Mayor of Cleveland,
d)When he ran for mayor of Cleveland in 1968,
e)In 1968 he had run for mayor of Cleveland, and
正解はd)です。疑問点はc)の駄目は理由です。
　c)の方が口語に近い気がしますが、文法的或いはGMAT的に悪い箇所が分からないので、どなたか教えて頂けますか。

http://tools.geocities.co.jp/CollegeLife-Cafe/6302/@geoboard/