Which of the following subsets in the set of polynomials R[x] is not closed for the operation of polynomial addition?(a) {p ∈ R[x] | p(0) = }(b) {p ∈ R[x] | p' = 0 }(c) {p ∈ R[x] | p(1) = 0 }(d) {p ∈ R[x] | p(1) = p(0) }(e) R2[x]