Once made exclusively from the wool of sheep that roam the Isle of Lewis and Harris off the coast of Scotland, Harris tweed is now made only with wools that are imported, sometimes from the mainland and sometimes they come—as a result of a 1996 amendment to the Harris Tweed Act—from outside Scotland.
A. sometimes from the mainland and sometimes they come "sometimes from X" and "sometimes they come" are not parallel. Eliminate.
B. sometimes from the mainland and sometimes Correct answer - parallelism is maintained and no new errors are introduced.
C. and come sometimes from the mainland or sometimes Usage of comma + "and" is not followed by an independent clause since it has no subject. Eliminate.
D. from the mainland sometimes, or sometimes it comes "from the mainland sometimes" and "sometimes it comes" are not parallel. Eliminate.
E. from the mainland sometimes, or sometimes coming Same parallelism error as in (A) and (D). Eliminate.