Sentence Correction

OG explanation is not clear to me...pls help me with this.

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.