(A) twice as fast as
(B) twice as fast as it was in
(C) twice what it was in
(D) two times faster than that of
(E) two times greater than
The two objects compared here are "in the 1980's" and "in the 1970's", and so we need "in", thus (A), (D), (E) are out.
Between (B) and (C), "twice as fast as" looks better.
I vote for (B).
I agree with you in that "greatr rate" is better than "faster rate".
I don't think (A) is a perfect answer, but is still the best answer.
Auge um Auge, Zahn um Zahn !