4. Let G be a pseudorandom generator with expansion factor (n) > 2n. In each of the following cases, say whether G' is necessarily a pseudorandom generator and explain why or why not. Here, "|| denotes string concatenation. 1 (a) Define G'(s) = s||s. Describe and formally analyze an attack if G' is not a pseudorandom gener- ator. (b) Define G' (s) G(s1 Sn-2), where s = 8s and si represents the i-th bit of s. (c) Define G'(s) = G(s)||G(s + 1).