请问prep2-48

答案是B。

sometimes前面的逗号是做什么的呢？

做题目的时候看了半天，不甚明了。

感觉有了逗号，这个sometimes引导的短语，语法现象很难解释？

48.        (27050-!-item-!-188;#058&003400)

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

(B) sometimes from the mainland and sometimes

(C) that come sometimes from the mainland or sometimes

(D) from the mainland sometimes, or sometimes it comes

(E) from the mainland sometimes, or sometimes coming