Question

The terms of the Paris Peace Accords _____.

called for the unification of Vietnam in ten years
required North Vietnam to give economic aid to South Vietnam
required South Vietnam's Nguyen Van Thieu to resign
were not much different from the October 1972 agreement

Answer 1

I can narrow it down to a or b for you.

Answer 2

The United States, South Vietnam, Viet Cong, and North Vietnam formally sign “An Agreement Ending the War and Restoring Peace in Vietnam” in Paris.

Unification means to become 'united' or made a 'whole'

So because of those two facts, I'd say the answer is A. :)

Answer 3

that is correct. I knew the answer, I just usually start by narrowing down the choices for them.