Use reasoning to lead to the answer of the following question:
He was at the gym trying to build muscle, what is it called that he is trying to build muscle on?\nOptions:\n- body of animal\n- arm\n- bodybuilder\n- body of dog\n- human body
 Reasoning process:
User
People work on their body in gyms. Muscles are part of a human body. Therefore, the final answer is human body.
Assistant