AMRINDER, this is definitely one of those sentence correction questions in which we are choosing the best of five relatively poor answer choices. In fact, I don't think that this question reasonably reproduces an actual GMAT problem. That said, I'll still briefly discuss my process of eliminatin (because that's the kind of fellow I am!).
Choices D and E incorrectly use the possessive adjective
Black's rather than the plural noun
Blacks.
Choice C contains several incorrect constructions. The two "which phrases" stand out as particularly erroneous. "Which phrases" must be separated by commas and normally include nonessential sentence information.
Choice B indicates that there exists some unidentified African land "symbolizing the possibility of freedom to [Marcus Garvey], but does mention which land this may be!
Choice A is the best of the worst ("the cream of the crap!)
-dan
A controversial figure throughout most of his public life, the Black leader Marcus Garvey advocated that some Blacks return to Africa, the land that, to him, symbolized the possibility of freedom.
(A) that some Blacks return to Africa, the land that, to him, symbolized the possibility of freedom
(B) that some Blacks return to the African land symbolizing the possibility of freedom to him
(C) that some Blacks return to Africa which was the land which symbolized the possibility of freedom to him
(D) some Black’s returning to Africa which was the land that to him symbolized the possibility of freedom
(E) some Black’s return to the land symbolizing the possibility of freedom to him, Africa