Final Answer:
Moving parts at a joint so that the angle between them increases and the parts move farther apart (straightening the knee) is called A. Extension
Step-by-step explanation:
Extension is the movement of body parts at a joint that increases the angle between those parts and moves them farther apart. In the context of the example given (straightening the knee), extension would be the correct term. This movement is the opposite of flexion, which decreases the angle between body parts, bringing them closer together.
Abduction involves moving a body part away from the midline of the body, and adduction involves moving a body part toward the midline. These movements are different from extension and flexion, which specifically refer to changes in the angle between body parts at a joint.
The correct option is A.