In the given excerpt from "The Open Window," Framton Nuttel's assumptions about the strangers who live there are influenced by his interpretation of the room's atmosphere. Specifically, he "admits" to knowing only Mrs. Sappleton's name and address but feels that there is something about the room that "seemed to suggest masculine habitation." This leads him to assume that Mrs. Sappleton must either be married or widowed. Therefore, the correct answer is:
He assumes Mrs. Sappleton must either be married or widowed.