How long were U.S. Marines under siege at Khe Sanh?

The correct answer is 77 days, which signifies the duration of the siege at Khe Sanh, an important battle during the Vietnam War. This siege began on January 21, 1968, and lasted until March 8, 1968, when U.S. forces were finally relieved. The Marines stationed at Khe Sanh were subjected to heavy artillery fire and constant enemy attacks, reflecting the intense combat conditions of the Vietnam War.

The duration of the siege is critical for understanding the strategic significance of the engagement, as it exemplifies the resilience of the Marines and the challenges they faced in maintaining their position against overwhelming odds. The situation at Khe Sanh was a pivotal moment in military history, showcasing the endurance and determination of U.S. forces in a protracted battle.

In terms of the other choices, they do not reflect the accurate timing of the siege, which is crucial for grasping the historical context of this event.