Answer:
Among the options given here, the good choice is:
C. Congress refused to support South Vietnam any longer.
Step-by-step explanation:
It was only until 1975 that Congress refused a last-minute request from president Gerald Ford for $300 million in aid for South Vietnam, the American ally in the conflict there. The request was made just weeks before the fall of Saigon to the North Vietnamese army on April 30, 1975. There is a long debate among US historians, intellectuals and politicians about whether Congress is to blame for "losing" Vietnam. As with other controversial issues, there is no unanimous conclusion.