Which one of the following Boolean expressions is a tautology?

• A. (p ∧ q) ∨ (p ∧ ~q)
• B. (p ∨ q) ∨ (p ∨ ~q)
• C. (p ∨ q) ∧ (p ∨ ~q)
• D. (p ∨ q) ∧ (~p ∨ ~q)