Concept:The contrapositive of a conditional statement reverses and negates both parts.Explanation:Let p represent "Stephen is good at Mathematics".Let q represent "Stephen is intelligent".Original conditional: p→q.Contrapositive: ∼q→∼p.In words: If Stephen is not intelligent, then he is not good at Mathematics.Compare this with the given options.Option C matches exactly.Answer:C. If Stephen is not intelligent, then he is not good at Mathematics.