As in so many mystery novels, Roger Ackroyd is set in a small, isolated community where everybody knows everybody else. The isolated, close-knit setting 1) suggests that the criminal is someone who everybody knows, and 2) creates a paranoid, suspenseful mood, since the criminal is hiding a big secret from their neighbors. It’s also telling that the owners of the two most “important houses” in town are also the two main victims of the novel.
has a natural insight about what the words likely suggested.
The third sentence down is the right answer. It doesn't use slang.
Disappointed and upset are very similar. If your parents told you you were getting ice cream and then you didn’t, you’d be disappointed, which could also be described as upset.