Determine whether or not the following claim is true for

Question

Determine whether or not the following claim is true for all regular expressions r₁ and r₂. The symbol ≡ stands for equivalence regular expressions in the sense that both expressions denote the same language.

(a) (r₁^*)^* ≡ r₁^*

(b)  r₁^*(r₁ + r₂)^∗ ≡ (r₁ + r₂)^∗

(c) (r₁ + r₂)^∗ = (r₁^*r₂^*)^∗

(d) (rs +r)^*r = r(sr + r)^*

All of the above true, I need proofs that I can understand and apply to similar questions.