Which of the Following Is a Core Question Addressed by Singer

Which of the following is a core question addressed by Singer?

A) How do the effects of our actions on the environment of nonhuman beings figure in our deliberations about what we ought to do?
B) Is it morally permissible to place less value on the interests of non human animals than the interests of human animals?
C) Is it morally permissible to raise and slaughter nonhuman animals for food?
D) All of the above