World war i was an important factor in advancing the cause of women's suffrage because a. too many men were serving in the military overseas to have meaningful elections without the participation of women. b. president woodrow wilson and members of congress believed that women would support the war effort if they were granted the right to vote. c. the peace treaty that stopped the fighting required all countries to give women the right to vote. d. a number of european nations threatened to refuse military assistance to the united states unless women were given the right to vote. e. soldiers returning from service began to demand the right to vote for their wives.

None of these answers are really what got the XIX amendment passed. It was the dogged determination of women who finally over a period of 6 decades that got the vote for women. Wilson was against it for many years, but changed his mind when Carr convinced him that Women's voting rights was a good thing. Usually the vote was gained, it is written in many places, because women contributed a great deal to the war effort.

Why it was given at the state level (Wyoming, Utah for example) is not clear to me. Why there before Federal rights were gained is a mystery.

answer D is utter nonsense. by WWI, America did not need help from anyone. Not D.

I don't think E is any better. Women's right to vote was mocked by almost every newspaper of the time. Not E

C?  Many countries gave women the right to vote after 1920. There were some that gave it before (Canada for example, granted the vote in 1917).
Eliminate C.

I think by a hair's width the answer is B. The war was over by 1920. But I wouldn't be surprised if it was A.

B <<<< reluctantly the answer.