Sentence Correction

Although various eighteenth- and nineteenth-century American poets had professed an interest in Native American poetry and had pretended to imitate Native American forms in their own works, until almost 1900, scholars and critics did not begin seriously to study traditional Native American poetry in native languages.

(A) until almost 1900, scholars and critics did not begin seriously to study
(B) until almost 1900 scholars and critics had not begun seriously studying
(C) not until almost 1900 were scholars and critics to begin seriously to study
D)it was not almost until 1900 when scholars and critics began to seriously study
E)it was not until almost 1900 that scholars and critics seriously began studying



Hello, everyone~

I am not very sure about this question. OA is E

I found C D seem to be correct for me. I have searched the previous posts and they say C D are wrong because of the "split indefinite". But I think there are other reasons because the "split indefinite" is not enough to rule out C & D. For example, in C "were to do" structure seems bad to me, and in D I think the "when" structure change the original meaning. However, I'm not quite sure about these.

Any experts can help me clarify that??