Answer: C) pitching the body forward, D) rocking from side to side, and E) sitting with the back humped.
Explanation: When riding a bicycle it is very important to have the correct posture, in order to avoid injuries. From the given options, the steps that a bicycle rider should avoid are: pitching the body forward, and sitting with the back humped, because it isn't the right posture and could produce back pain; and rocking from side to side, because it makes harder to mantain de balance when riding.
