Answer: C) Claim of cause and effect.
Explanation: a claim of fact or definition is a statement about a fact or a historical event, and it should be debatable and have factual evidence that supports it. A claim of solutions of policy is a statement about whether or not an action should be taken to improve or to solutionate a situation. A claim of cause and effect is a debatable claim about the causes or consequences of an action, this last one corresponds to the given example, because the debate will be if listening to books on tape can cause or not an improvement in the vocabulary and pronunciation of language learners.