Concept:The radius and ulna are the two long bones that form the forearm, which is also called the lower arm.Explanation:The upper arm contains only one bone, the humerus.The pectoral girdle is made up of the clavicle and scapula.The pelvic girdle consists of the hip bones.In the lower arm, there are two parallel bones: the radius and the ulna.Therefore, radius and ulna belong to the lower arm.Answer:D. lower arm