Choice C is the best answer. In lines 36-39("women...in"), Stanton states that society contains hardly any women in the "best sense," and clarifies that too many women are "reflections, varieties, and dilutions of the masculine gender." Stanton is suggesting that there are few "best," or genuine, women who are not completely influenced or controlled by men.
Choices A, B, and D are incorrect because in this context "best" does not mean superior, excellent, or rarest.