Which revolutionary party did most peasants support?
a. the socialists
b. the communists
c. the social revolutionaries
d. the constitutional democrats

The revolutionary party which was most supported by the peasants were actually the social revolutionaries - C.

The social revolutionaries were a group of people who argued for a new social and political system but tot achieve which, first there would have to be a revolutionary war, where they would be able to overthrow the old government. 

Generally speaking, the peasants mostly supported the "B. the communists," since the communists promised them that they would have better economic growth under the new system. 

The United States of America,  this was known as the Great Depression.