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

OA E
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What is the difference between choice A & C regarding their placement of the prepositional phrase?

The OG has mentioned that the phrase "until almost 1900" will cause confusion because it can be used to modify either the first verb or the next verb. But why??

However, the placement in choice B can eliminate this problem.

It looks like,
(A) ....,until almost 1900,....(non-essential info.)
(B) ............, until almost 1900....... (essential info.)

What causes the difference? Is there any rule that can be followed so that we can figure out what the prepositional phrase is intended to modify?

Thanks in advance.