all 3 are correct hence ans should be D
(a) (r + s)* = (s + r)* any string conrstructed by LHS can also be created by RHS and vice versa like λ, r,s,rr,ss,rsrs..
b) (r*)* = r* again valid as (r*)* = r*.r*.r* .....possible strings are r,rr,rrr,rrrr... including λ;
c) (r* s*)* = (r + s)* LHS= (r*s*)(r*s*)(r*s*)...... so strings like λ,r,s,rs,rsrs,srsr,rrrr,ssss,...are generated while RHS (r+s)* =(r+s)(r+s)...can also generate λ,r,s,rs,rsrs,srsr,rrrr,ssss