For a Function f : A → B such that n(A) = a, n(B) = b (a,b∈N) then which of the following statements must be CORRECT ?

(A) If function is one - one, onto, then a>b

(B) If function is one - one, into, then a<b

(C) If function is many - one, onto, then a>b

(D) If function is many - one, into, then a<b