-doing vs -by doing 求牛牛解释

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The organic foodindustry has organized a successful grassroots campaign—using Web sites,public meetings, and also mass mailings—that have convinced the Departmentof Agriculture to change the proposed federal regulations for organically grownfood.

A.     using Web sites, publicmeetings, and also mass mailings—that have convinced

B.     using Web sites, publicmeetings, and mass mailings—that has convinced

C.     by using Web sites,public meetings, and mass mailings—in convincing

D.    by the use of Web sites, public meetings, as well as mass mailings—thatconvinced(B)

E.     which used Web sites,public meetings, and mass mailings—in convincing

这道题答案选B，对于这题的答案我没有问题。问题是，在B选项前面加上一个by，会有什么不同的意思吗？还是没有很大影响？
请教牛牛。

lifeisanart

Ron的解释：
* if you say "subject + clause + BY VERBing", then "by VERBing" must explain HOW the main clause occurred.
e.g.
i prepared for the test by reviewing takeaways on the MGMAT forums.
note that the boldface clause describes HOW i prepared for the test.

choice (c) means that using websites, etc. was how the industry organized the campaign -- in other words, they used the websites and public meetings to organize the campaign in the first place. that's an incorrect meaning.
(the campaign ITSELF used these things; the correct modifier in (a) and (b) shows that relationship.)

* if you say "subject + clause + IN VERBing", then subject + clause must be an ACTUAL PART of the action of VERBing.
e.g.
i solved all the problems in OG12 in preparing for the GMAT.
--> notice that solving the problems IS ACTUALLY PART OF preparing for the test.

choice (c) fails here, too, since organizing the campaign (the main clause) is not ACTUALLY PART OF convincing the government.

从句以上理解的话，by using 指通过利用网站，公众集会和大众邮件的方式，我们组织了一场成功的活动。
                  using 指我们组织了一场成功的活动，采用了网站，公众集会和大众邮件的方式。
看到了吗，前一个有强烈的因果联系，后一个表现出伴随关系，意思理解是不一样的。
至于in cnvincing 的问题上面Ron已经讲得很清楚了。
就像baby姐一直提倡的，语意是王道啊

olivia瓜瓜

没注意过这个知识点，同等牛牛解答，不过感觉是应该不可以的， by doing 通常是 A do sth by doing sth 。
这里这个破折号的意思，这里的ING是做状语还是做定语修饰呢？？