GMAT Sentence Correction (SC) | While studying the genetic makeup of corn, a new class of mutant genes

A. a new class of mutant genes was discovered by BarbaraMcClintock, a discovery which led
B. a new class of mutant genesin corn were discovered byBarbara McClintock, leading
C. Barbara McClintock discovered a new class of mutant genes, andit led (ambiguity, what is "it" referring to? the genes or the discovery?)
D. Barbara McClintock discovered a new class of mutant genes, a discovery that led
E. Barbara McClintock, who discovered a new class of mutant genes,leading (the sentence
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