A young woman fell and hit her knee. Examination: valgus test +ve. What ligament was most probably injured?

The key is B. Medial collateral. [The valgus stress test involves placing the leg into extension, with one hand placed as a pivot on the knee. With the other hand placed upon the foot applying an abducting force, an attempt is then made to force the leg at the knee into valgus. If the knee is seen to open up on the medial side, this is indicative of medial collateral ligament damage].