Which of the following institutions completes the excerpt below?

the is in operation. i am in favor of going in. this is the supreme test. shall we act in concert with the free nations of the world in setting up a tribunal which would avert war in the future? …we must say in language which the world can understand, whether we shall participate in the advancement of a cause which has in it the hope of peace and world reconstruction, or whether we shall propose to follow the old paths trod by the nations of europe — paths which always led to fields of blood.

a. league of nations
b. mandate system
c. bolshevik revolution
d. union of soviet socialist republics