Which of the following are tautologies? A. (p ∨ r) → p B. p → (p ∧ r) C. ~p → (p → r) D. (p ∧ r) → (p → r) E. ~(p → r) → p

1. AA, B Only
2. BA, B, C Only
3. CB, C, D Only
4. DC, D, E Only

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Correct answer: D. C, D, E Only

Explanation

A fails when p is false and r true; B fails when p is true and r false. C: if ~p then p → r is vacuously true. D: if p ∧ r then p → r holds. E: ~(p → r) means p ∧ ~r, which implies p. So C, D and E.