Which of the following is always true?

Since, ~(p∨q)≡(~p∧~q) and ~(p∧q)≡(~p∨q)So,. option (b) and (d) are not true.(p→q)≡p∧~q so option (c) is not true. p→q~p∨q~q→∼p≡[~(~q)∨~p]≡q∨~p≡∼p∨q p→q≡∼q→∼p