SC Correction Explanation Validation - OG 674

674. Air traffic routes over the North Pole are currently used
by only two or three planes a day, but it was found
by a joint CanadianRussian study to be both feasible
as well as desirable if those routes are opened to
thousands more commercial planes a year.

(A) Air traffic routes over the North Pole are
currently used by only two or three planes a day,
but it was found by a joint CanadianRussian
study to be both feasible as well as desirable
if those routes are opened to thousands more
commercial planes a year.

(B) Currently used by only two or three planes a day,
a joint CanadianRussian study has found that if
air traffic routes over the North Pole are opened
to thousands more commercial planes a year, it
would be both feasible and desirable.
(C) A joint CanadianRussian study, finding it to be
both feasible as well as desirable to open air
traffic routes over the North Pole, which are
currently used by only two or three planes a day,
to thousands more commercial planes a year.

(D) Although air traffic routes over the North Pole
are currently used by only two or three planes a
day, a joint CanadianRussian study has found
that opening those routes to thousands more
commercial planes a year is both feasible and
desirable.

(E) With air traffic routes over the North Pole
currently used by only two or three planes a
day, opening those routes to thousands more
commercial planes a year has been found by a
joint CanadianRussian study as both feasible
and desirable.


I rejected A- because of two reasons 1. Incorrect Idiom Both X as well as. 2. Because It was being used as a dummy pronoun here, and hence must either refer to an infinitive phrase or to a that/who clause.

I also read somewhere on GMAT Club forum that there is a tense mismatch in A. Is that correct?