The following are three valid arguments. Establish the validity of each by means of a truth table. In each case, determine which rows of the table are crucial for assessing the validity of the argument and which rows can be ignored.
(a) [p ∧ (p → q) ∧ r] → [(p ∨ q) → r]
(b) [[(p ∧ q) → r] ∧ ¬ q ∧ (p → ¬r)] → (¬p ∨ ¬q)
(c) [[p ∨ (q ∨ r)] ∧ ¬ q] → (p ∨ r)