The correct answer is A. She could cause an injury.
When Rosa bounces up and down while stretching, it can lead to overstretching the muscles beyond their natural range of motion. This can strain the muscles and potentially cause injury. It's important to stretch in a controlled and static manner to avoid putting excessive stress on the muscles and joints. Bouncing during stretching is not recommended as it can increase the risk of injury rather than improving flexibility or strength. Stretching should be done gradually and held in a stable position to safely improve flexibility and prevent injuries.