Final answer:
The gracilis muscle is responsible for adducting the thigh at the hip joint and flexing and rotating the lower leg at the knee joint, making it the correct answer for the given actions.
Step-by-step explanation:
The muscle that adducts the thigh at the hip joint, and also flexes and rotates the lower leg at the knee joint is the gracilis muscle. Not only does it adduct the thigh, but it also contributes to leg flexion at the knee. The gracilis muscle allows for the crossing of the legs, which is an action involving thigh adduction and knee flexion. It's important to note that while muscles like the gluteus maximus, piriformis, and tensor fascia latae do play roles in moving the thigh and lower leg, none of them performs the same combination of actions as the gracilis muscle.