Which sentence uses punctuation correctly?

a. mrs. nelkin, who lives next door to my aunt, owns three dogs.

b. mrs. nelkin, who lives next door to my aunt owns three dogs.

c. mrs. nelkin who lives next door to my aunt owns three dogs.

The sentence that uses punctuation correctly is A) Mrs. Nelkin, who lives next door to my aunt, owns three dogs.
Appositive phrases, such as who lives next to my aunt need to be separated with commas from the rest of the sentence. 

Refute it, showing why it is mistaken—an apparent but not real problem; acknowledge its validity or plausibility, but suggest why on balance it's relatively less important or less likely than what you propose, and thus doesn't overturn it; concede its force and complicate your idea accordingly—restate your thesis in a more exact, qualified, or nuanced way that takes account of the objection, or start a new section in which you consider your topic in light of it. this will work if the counterargument concerns only an aspect of your argument; if it undermines your whole case, you need a new thesis.