Unhappy triad

A 17-year-old male comes to the emergency department because of severe left knee pain for an hour. He was playing football when an opposing player hit the lateral aspect of his knee. He was unable to finish the game because of pain, and he feels instability in his knee. Examination of the knee shows a large effusion. There is tenderness along the medial joint line, and Lachman test is positive. Which of t