Which best states a theme of "the lottery"? a. seemingly ordinary people can do horrible things. b. people are friendlier in small towns than in cities. c. traditions people remain civilized. d. lotteries are needed to ensure a good harvest.

A. Seemingly ordinary people can do horrible things.

The lottery itself is shown to be a bad thing, though the characters do not realize it, so it is a tradition that leads them to do something uncivilized and we as an audience know they do not actually ensure a good harvest. As well, it's clear that they are not friendly since they are killing their citizens. Thereofre B, C and D are incorrect.
However it does show us that ordinary people can do terrible things, because we don't know what the lottery is exactly. So all the citizens seem like totally ordinary people, thus the reveal at the end shows us what these "totally ordinary people" are capable of.