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The key factor in the decision of the U.S. to enter World War I was

AA long-standing friendship with Great Britain
BAmerican prejudice against German immigrants
CThe political ambition of Woodrow Wilson
DGermany's resumption of unrestricted submarine warfare against the U.S.

Verified Answer :

The key factor in the decision of the U.S. to enter World War I was "d. Germany's resumption of unrestricted submarine warfare against the U.S.," since this led to the sinking of the Lusitania, which had many US citizens on board. 

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