What did most americans understand before their country entered world war i?
o that the war would not last long
o that the war would cost american lives
o that the war would the us economy
o that the war could be won by the us alone

None of the options here are good.

Explanation:

American public opinion was divided and there were many views before the war.

The US joined the Allied effort, so nobody thought it could win alone.

Economic benefit was never a major thinking current in public opinion in the USA.

People didn´t expect their country to suffer so many casualties, but that a country will suffer causalties if it enter a war is obvious.

When the US entered WWI, the conflict had been going on for 3 years already, so people could not expect the war to be short-lived.

i believe it was spain