Why was the Zimmerman telegram a turning point in many US citizens' attitude about entering the war?
A.
The telegram revealed that Russia was preparing to enter into an alliance with Austria-Hungary.
B.
The telegram's author, Arthur Zimmerman, wrote the telegram while spying for the German government.
C.
The telegram exposed a code that would make US messages easily decipherable by other countries.
D.
The telegram said that Germany would cede United States territory to Mexico if Mexico cooperated with the German military.