This must be British English. In American English you would use the phrase "thick black hair." In American English, all the choices are correct. C is rarely used, but, when used, it is typically when another person is described, especially in a story, to evoke a strong image. Obviously B is correct because, when he was in the army his head was shaved, and when he left the army "the young man grew thick black hair." D is correct because it signifies the way the young man prefers his hair, as if he was making a fashion statement. Example: The young man wore thick black hair. He tied it into a small ponytail to provoke the police. Corrections: young NOT yound ...why the other three ARE not correct NOT ...is not correct