The correct answer is (B) taken.
The sentence is expressing a hypothetical or unreal condition in the past. It uses the past perfect tense ("had had") to indicate a condition that didn't actually happen. In this case, the verb "take" needs to be in the past participle form to match the past perfect tense.
Therefore, the correct form of the verb is "taken." The sentence should be: "Nancy would have taken a vacation if she had had enough money."
