Which of the following events forced the united states into world war 1?

a) communist revolution in russia
b) germany's resumption of unrestricted submarine warfare
c) british blockade of europe
d) germany's invasion of belgium

Correct  B. Germany's resumption of unrestricted submarine warfare.

Context/detail:

Public outrage in the US against the Germans swept the nation following the sinking of the British ocean liner, Lusitania, which had happened in May, 1915.  When a German U-boat (submarine) sank the Lusitania, over 1,000 persons were killed, including more than 100 Americans. The passenger liner was targeted by the Germans because they suspected weapons were being shipped to Britain in the cargo hold of the ship.

Germany managed to stave off American entry into the war at the time by pledging to stop submarine attacks.  But two years, later, beginning February 1, 1917, the Germans resumed such attacks. This poised America to go to war.  

In addition, British intellegence intercepted and decoded a telegram (known as the "Zimmermann Telegram") that showed Germany was trying to secure Mexico as an ally against the United States.  The revelation of this plan inflamed feelings in the United States.  The telegram was sent in January, 1917.  In March, 1917, German Foreign Secretary Arthur Zimmermann admitted the telegram was, in fact, sent by his office.

In April, 1917, the US declared war on Germany in response to the German's submarine warfare and the Zimmermann Telegram.

honestly you should get that checked out because it really isn't normal