What of the Following Best Captures Singer's Response to Sidgwick

What of the following best captures Singer's response to Sidgwick and Urmson's objection that if we tell people not to murder others and to give to famine relief, they will do neither, but if we tell them not to murder, they will at least do that?

A) Singer argues that if we tell people to give to famine relief, then they will do that, whereas we need not tell people not to murder because the norms against murder are already firmly entrenched.
B) Singer argues that what people actually do is completely independent of what they ought to do, and so Sidgwick and Urmson's objection is irrelevant.
C) Singer argues that the norms against murder and the norms to give to famine relief are intertwined and cannot be separated because both are about preventing deaths.
D) Singer argues that moral standards themselves set expectations that affect people's decisions and actions, so setting expectations to give everything you don't need to famine relief may lead to people doing so.