The anterior cruciate ligament (ACL) is one of the major knee joint ligaments in

The anterior cruciate ligament (ACL) is one of the major knee joint ligaments in people, and damage to this ligament is fairly common in athletes. An ACL tear is most often a sports-related injury but can also result from accidents, falls, and work-related injuries. Most sports-related ACL tears occur when a person pivots or lands from a jump.

Based on this information as well as your knowledge of ligaments, which of the following occurs in an athlete who has a torn ACL?
A) inability to contract the quadriceps
B) inability to relax the quadriceps
C) instability or weakness of the knee joint
D) rapid firing of all the neurons involved in the affected motor unit