what was the effect of the u. s. troops leaving south vietnam?

a) south vietnam won its independence and became a democratic nation

b) south vietnam move towards a capitalist economy

c) south vietnam was reunited by force with north vietnam and became a single communist nation

d) south vietnam continued to be anti-communist

Correct

Explanation:

The US had been supporting South Vietnam against the communist North Vietnam.  Ultimately, US President Richard Nixon proposed drawing down US involvement in the war and seeking "peace with honor," as he put it.  

Once the US forces withdrew (after a long, unsuccessful struggle), it was too late for the South Vietnamese to stave off the victory of the North Vietnamese and Viet Cong forces.  The US withdrew its forces from Vietnam in 1973.  By 1975, Saigon, the capital of South Vietnam, fell to the North Vietnamese communist forces.  South Vietnam unconditionally surrendered to North Vietnam on April 30, 1975.  All of Vietnam became united under communist control.

a memoir is the correct answer