The answer to your question is option b, a base. This is because the question clearly tells you that one reactant is an acid. Then, it tells you that an acid plus something gives you a salt and water, as products
From background knowledge, we know that a base plus acid gives you a salt and water. The hydroxide ions from the base neutralise the hydrogen ions from the acid, which gives you water ( as it has a pH of 7).
Therefore, your answer is b, a base
