The correct answer is D

Explanation

Choice (D) is correct. It avoids the comma splice error of the original by combining the two independent clauses that were improperly joined by only a comma (“There are many famous quotations previously credited to ‘Anonymous’” and “researchers have discovered that they were in fact written by female authors”) into one sentence consisting of a main clause (“Researchers have discovered”) and a dependent clause (“that many famous quotations previously credited to ‘Anonymous’ were in fact written by female authors”).