Final answer:
The LCL and MCL are taut when the knee is in full extension, serving to stabilize the knee by resisting hyperextension and rotation (option a).
Step-by-step explanation:
The LCL (Lateral Collateral Ligament) and MCL (Medial Collateral Ligament) are taut when the knee is in full extension. These ligaments are on the sides of the knee and become tight to help stabilize the joint in this position. In full extension, the femur undergoes a slight medial rotation in relation to the tibia, which helps to lock the knee into its most stable position. The LCL and MCL serve to resist hyperextension or excessive rotation, while the anterior cruciate ligament prevents hyperextension, and the posterior cruciate ligament supports the knee when it is flexed and weight-bearing.
Hence, the answer is option a.