Simply analyze, in option B, what do you think THEY points to and you will know why B is incorrect.

ronnie1985 wrote:I am not convinced by the Official Explanation. the question stem is attached herewith and the OA is (D)

I really like this question as an example of a neat device that the authors of the GMAT employ - they know that your eyes will go directly to the underlined portion, so they can hide valuable information outside the underline.

Here, the sentence begins with the phrase "Since 1986". But you probably ignore that part and go on to the answer choices.

Keep in mind, though, that the verb tenses "began" and "have began" depend on the timeline. And "Since 1986" means "back then AND ongoing". "Began" is wrong - it's straight past tense with no ongoing nature, so it conflicts with "since" as the timeline for the whole sentence. That's a fatal flaw in (B).

Even more important - see what the GMAT just did to you. It knew that you would blow through the modifier outside the underline, and it gave you a few answer choices that didn't require you to notice it in order to eliminate them. When you're down between a couple answers, go back and check to see if something further away from the underline really matters as you make that decision. And because you know that verb tenses are testable, when you see a phrase that indicates a timeline, know that it's probably going to be important!