Can a pariciple, gerund, or an infinitive be used as a noun substitute?

What is the climax of chapter 2 of the the sound and the fury? a. the compsons sell their plot of land to send quentin to harvard. b. quentin drops out of school. c. quentin commits suicide. d. caddy gets pregnant.

Aman lives on the twelfth floor of an apartment building. every morning he takes the elevator down to the lobby and leaves the building. in the evening, he gets into the elevator, and, if there is someone else in the elevator -- or if it was raining that day -- he goes back to his floor directly. otherwise, he goes to the tenth floor and walks up two flights of stairs to his apartment.

How does dr. king defend the claim he makes in paragraph 9