This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lower Extremity, Subject name: Anatomy
A 55-year-old cowboy is admitted to the emergency department after he was knocked from his feet by a young longhorn steer. MRI examination reveals a large hematoma in the knee joint. Physical examination reveals that the patient suffers from the "unhappy triad" (of O'Donahue). Which of the following structures are involved in such an injury? 
Select and explain. 
A. Medial collateral ligament, medial meniscus, and anterior cruciate ligament, B. Lateral collateral ligament, lateral meniscus, and posterior cruciate ligament, C. Medial collateral ligament, lateral meniscus, and anterior cruciate ligament, D. Lateral collateral ligament, medial meniscus, and anterior cruciate ligament
A: Medial collateral ligament, medial meniscus, and anterior cruciate ligament
Answer: A: Medial collateral ligament, medial meniscus, and anterior cruciate ligament 
Explanation: The "unhappy triad" (of O'Donahue) is composed of the medial collateral ligament, medial meniscus, and anterior cruciate ligament. Sudden, forceful thrusts against the lateral side of the knee put tension on the medial collateral ligament, which can then rupture. The medial meniscus is attached to the medial collateral ligament so that it then tears. The anterior cruciate ligament resists hyperextension of the knee; thus, it is the third structure that breaks in the "unhappy triad" of the knee.