The correct option is D Something unsupportable to those who have absorbed the methods of science.
Astrology is mentioned as a quackery. Quackery is something that claims to be true but is actually based on falsity. He implies that people are fooled by astrology, but he also implies that there are other more dangerous ideas. So we eliminate A, B and D. It is not likely that astrology is a failure of science but it is something that scientists would not approve of. Hence answer C.