GMAT Sentence Correction (SC) | Re: Even though eighteenth- and nineteenth-century American historians had

Even though eighteenth- and nineteenth-century American historians had professed an interest in Native American history and had pretended to imitate Native American styles in their own works,until almost 1900, historians did not begins seriously to research traditional Native American history in native languages.
A. until almost 1900, historians did not begins seriously to research
B. until almost 1900 historians had not begun seriously researching
C. not until almost 1900 were historians