For what purpose would authors use evidence to support their claims

To verify that what they're saying is correct

Explanation:

Authors want to use only true information in their work, so they look for evidence that deals with the same subject they are talking about. These evidences will serve to support their claims and show that these statements are correct. The result is that the work of these authors will be more credible with the public.

the correct answer is the first option "the bolkshevik revolution". the passage makes reference to many of important events that occured in the revolution, such as the assemblies, in this case the animals are gathered in an assembly after a protest, the murder of fellow partners, the speeches given by the leader of the revolution, among other aspects. the last choice is possible, but in this passage in particular it is not emphasized the fight between the characters, that is the two pigs, that represent lenin and stallin.