German Submarines Began Sinking Unarmed and Unresisting Merchant and Passenger

Multiple Choice

German submarines began sinking unarmed and unresisting merchant and passenger ships without warning

A) when the United States entered the war.
B) in retaliation for the British naval blockade of Germany.
C) in an effort to keep the United States out of the war.
D) because international law now allowed this new style of warfare.
E) in a last-ditch effort to win the war.