The correct answer is tone. Imagery is using vivid description while style is the personal type of narration like what words they use or grammatical constructions. Theme is the underlying idea while the voice is seen through the tone, whether it's dark and broody or joyful or anything similar.
Plot. Two migrant field workers in California on their plantation during the Great Depression—George Milton, an intelligent but uneducated man, and Lennie Small, a bulky, strong man but mentally disabled—are in Soledad on their way to another part of California
