Answer:
There is nothing wrong with this sentence.
Explanation:
All punctuation and grammar is correct.
B) The daily work continued; nay, it actually increased;
Something that is happening on a consistent basis. It also gives the feeling that it is work to make it persistent. In option B, the statement "daily work" indicates that something is done daily which supports the idea of persistent. The sentence containing the line "The daily work continued; nay, it actually increased" also includes the description "with an astonishing pertinacity." Pertinacity means persistent determination. The brain failing and life slipping away does not show any persistent determination. Also, the statement that she inquired with acute anxiety does not how any persistent determination.
I think thew answer is D. "The author supplies the rubuttel that quotes more current research". I'm not 100% sure but it was the best one i could think of. Hope it's right