According to the lecture of philosophical skepticism (PS), which of the following statements are true?

a. The position known as philosophical skepticism can be stated as follows: No philosophical claim is true or false.

b. One of the plausible replies to philosophical skepticism is that it's based on an invalid inference; that is, just because we haven't found the answer, it doesn't follow that there are no answers.

c. Philosophical skepticism appears to be paradoxical; that is, it states there are no right answers, and yet they are committed to the view that (PS), which is a philosophical claim, is true.

d. All of the above.

e. None of the above.