GMAT Sentence Correction (SC) | New, strong varieties of antibiotics

Here they test parallelism.
a) unintended effectsof killing benign bacteriaand the development of resistant strains of bacteria by earlier high-strength varieties.
Here, a verb (killing) and a noun (the development) are not of the sametype.

e)[the] killing of benign bacteriaand development of resistant strains of bacteria, which were unintended effects of earlier high-strength varieties.
The aforementioned problem is fixed when the verb (killing) becomes a noun (the killing) in the
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