When Appiah Says That Human Rights Are "Weakly Philosophically Grounded

When Appiah says that human rights are "weakly philosophically grounded," he most nearly means that

A) the idea that all humans have certain rights is difficult to defend philosophically.
B) declarations of human rights do not actually motivate anyone to do anything.
C) the concept of human rights does not depend on any specific metaphysical claim about their source.
D) despite the idea's widespread appeal, people do not have actually human rights.