Careful, vp101. The problem with B can't be "given reason," since that is used in A, too!

The issue is with "would," but this is a little tricky. For simpler clauses, it's easy: we don't use both "if" and "would" to mark the same hypothetical event. Rather, when using "if," we follow up with "would" to show the consequence:

If my car were stolen, I would be upset.

However, if our hypothetical/conditional has more than one action in it (as in the original Q), "would" may be appropriate:

If I thought that you would believe me, I'd tell you the whole story.

So what's the difference between this and the original? You might notice that here we're using what looks like past tense ("thought"), while in A and B we're using present perfect and present, respectively. Why the difference? My example is a hypothetical (subjunctive), while the original is a simple conditional. With conditionals, we don't even use "would" for the consequence:

If Karen's sandwich falls on the floor, she will still eat it. (It's a really good sandwich.)

Since the choices here are conditional and not subjunctive, we need to leave "would" out of the sentence entirely.

转自：https://gmatclub.com/forum/a-recent-court-decision-has-qualified-a-1998-ruling-that-workers-canno-207805.html#p1593308