Which one of the following Boolean expressions is NOT a tautology?

• A. \(((a→b)∧(b→c))→(a→c)\)
• B. \((a↔c)→(∼b→(a∧c))\)
• C. \((a∧b∧c)→(c∨a)\)
• D. \(a→(b→a)\)