Which of These Claims Is the Basis for an Argument

Which of these claims is the basis for an argument against legalizing polygamy?

A) All informed, consensual conduct should be legalized.
B) Legalizing polygamy raises the status of some people without downgrading the status of anyone else.
C) It is possible that all member of a polygamous union can offer informed consent.
D) Even if polygamy does not itself violate anyone's rights, its legalization is highly likely to do so, by contributing to oppression of women.