<p>It is still 50/50.</p>
<p>Caustic still has a definition of bitter and critical. Just because the first definition refers to a substance, doesn’t mean collegeboard can use it for the other definitions it has. In context, they are more likely referring to the caustic that means bitter and critical. Vehement means extremely angry with rancor, and hostility. This is an extreme, and if you read the passage, he was not extremely angry or hostile at all. In fact, he was criticizing aspects of the subject, and he was bitter at that too.</p>
<p>I understand that you may pick vehement, but you are only supporting that because you are biased to that answer after you chose it.</p>