prep1-182.The organic food industry has organized a successful grassroots campaign—using Web sites, public meetings, and also mass mailings—that have convinced the Department of Agriculture to change the proposed federal regulations for organically grown food.
A.using Web sites, public meetings, and also mass mailings—that have convinced
B.using Web sites, public meetings, 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—that convinced E.which used Web sites, public meetings, and mass mailings—in convincing
1.Note that choice B maintains the present perfect tense: "has organized a campaign ... that has convinced." We cannot use the simple past tense "convinced" here, as that tense would not mesh with the present perfect. Moreover, "in convincing" is weak; we want to express that this campaign did the convincing. "In convincing" indicates that this campaign was just part of what convinced the Department. That is not the intended meaning of this sentence.
2.the posts here, for the most part, aren't accurate, except for choice (a). a previous poster correctly stated that choice (a) has incorrect subject-verb agreement (singular subject, plural verb).
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the problem with (c) is NOT grammatical; the grammar of (c) is just fine. the problem with (c) is that it uses two different transitions incorrectly.
* 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.