Although he had looked through all the reference material on the subject, he still found it hard to understand this point and her explanation only ________ to his confusion.
句意： 尽管他查阅了关于这个问题的所有参考资料， 他仍然很难理解这一点， 且她的解释只是增加了他的困惑。 add to 增加。 amount to 总计。 因此， 本题的正确答案为 B。