What Had Happened in South Vietnam by the End of 1975

Multiple Choice

What had happened in South Vietnam by the end of 1975 following the Paris Peace Accords?

A) The conflict resumed between South Vietnam and North Vietnam but with little consequence or outright warfare for many years.
B) The South Vietnamese government invited North Vietnamese leaders to a summit, where they agreed to acknowledge Hanoi's authority in the South.
C) North Vietnam signed a second treaty with South Vietnam, agreeing to withdraw its remaining troops after American forces left.
D) North Vietnamese troops gained the upper hand over South Vietnam, successfully invading and capturing Saigon.
E) The United States reentered the Vietnam War once Gerald Ford had replaced Nixon as president because the situation in Southeast Asia was so dire.