Sentence Correction

When he had run for mayor of Cleveland in 1968, Carl Stokes won the
election, proving that an African American candidate can be elected in
a city in which African Americans constitute a minority of the population.
(A) When he had run for mayor 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

Plz let me know the OA with explanations....