GMAT Sentence Correction (SC) | QOTD: A new test for AIDS has proved

Hi,
I chose B , but on second reading of the option B revealed it is wrong option.
That in option B infers that the nation's blood supply was contaminated , that is not the intended meaning .
It was some blood that was contaminated which needs elimination from blood bank.
Option C removes this ambiguity as it clearly says blood that was contaminated.
Hope this helps

---