ETS对OG-83解释有问题吗？not just... but ...结构是否也正确？

memory09

请教，OG-83中，答案选的B，可以理解。但解释中说：To present these two causes, the sentence employs a formula that requires parallel elements: not just because of x, but because of y, with x and y assuming the same grammatical form. 答案是not just... but also...结构，ETS解释用的是not just... but ...结构。是ETS笔误还是2种结构都可以用？多谢了

In 2000, a mere two dozen products accounted for
half the increase in spending on prescription drugs,
a phenomenon that is explained not just because of
more expensive drugs but by the fact that doctors are
writing many more prescriptions for higher-cost drugs.
(A) a phenomenon that is explained not just because
of more expensive drugs but by the fact that
doctors are writing
(B) a phenomenon that is explained not just by the
fact that drugs are becoming more expensive
but also by the fact that doctors are writing
(C) a phenomenon occurring not just because of
drugs that are becoming more expensive but
because of doctors having also written
(D) which occurred not just because drugs are
becoming more expensive but doctors are also
writing
(E) which occurred not just because of more
expensive drugs but because doctors have also
written

memory09

多谢楼上的~

treewing929

其實 NOT JUST 同 NOT ONLY 意思差不多!