How did vietnamization lead to the end of the war?

a. north vietnam ran out of funds.
b. us troops surrendered.
c. south vietnam fell.
d. president nixon declared victory.

Even though both ww1 and ww2 were in many ways the same conflict with basically the same countries facing off against each other, the way each war started was significantly different. the question is how what were the differences on how they started

Powers of states the first letter of the answer is r.

What stalled germany's initial invasion into france in 1914