The answer is C.
A is not, because the cowboy's appearance is not relevant to his personality as a round character. Same general idea for B and D.
Answer:
A: To act as the subject of the main clause
The sentence that uses direct address is "Where are you going, Fred?".
Direct address in grammar means that you are speaking directly to a person or group of people either calling them by name, as in example, "Where are you going Fred?", or using the second person pronoun "you". As in the example above, the name is often separated from the rest of the sentence or question by a comma. For example, "Maria, I need you to finish your homework now."
When you talk to or about someone in a mocking tone, you're making fun of them in a nasty, mean way. But if you're a comedy writer or political satirist, a mocking attitude is a tool of your trade.
Swimming is a good sport it helps build muscle.
