GMAT Sentence Correction (SC) | Re: A new test for AIDS has proved helpful i n eliminating

Responding to a pm asking why C beats D . . .

This is not one of the GMAT's better efforts. The short answer to why D is wrong is that "proved helpful to eliminate" is incorrect. However, I'm not convinced that the modifier structure of D creates any problems. We're eliminating blood from the blood supply, and D simply adds a modifier to say that this blood is contaminated with the virus. No one is going to think that the virus is "from the nation's blood supply."

C is awkward
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