Final answer:
The best statement of a theme of Gilman's "The Yellow Wallpaper" is option A, which acknowledges the reduced role of women in marriage during the 19th century and critiques the broader societal oppression of women, as depicted in the story.
Step-by-step explanation:
The sentence that best states a theme of Gilman's "The Yellow Wallpaper" is A. Women in the 19th century often played a lesser role in marriage. This theme reflects the central idea of the story, which criticizes the suppressed role of women during the era and examines the effects of this oppression on the mental health of the protagonist. The narrative challenges the traditional power dynamics within marriage and the society's predisposition towards male authority over female autonomy. The story is also an indictment of the 'rest-cure' which was prescribed to women during that period and how this treatment, devoid of stimulus and control over one's life, led to the deterioration of the protagonist's mental state.
While C. A husband does not believe that his wife is sick, which leads to disastrous consequences, is one plot element of the story, it is not the overarching theme. The rest-cure, implied in choice B, is a significant element in the story, but the broader theme extends beyond just the issue of the right medicine or rest. As for D, the narrator's dislike for the yellow wallpaper is a symbol for the larger theme of the story - the constraints placed on women's minds and bodies - rather than a theme in itself.