Which of the following is a contradiction?

a) p→(q→p)≡p→(~q∨p)≡~p∨(~q∨p)≡(~p∨p)∨~q≡t∨~q≡t b) p→(p∨q)≡~p∨(p∨q)≡t∨q≡t c) p∨q→(~p∧~q)≡~(p∨q)∨(~(p∨q))≡~(p∨q) d) (p∨~p)→(q∧~q)≡t→c≡(~t∨c)≡c∨c≡cLHS≥1,   RHS≤1