In my opinion, the correct answer is D. She tried on several pairs, and she chose a blue and grey pair to replace her old shoes.
There are exactly 7 coordinating conjunctions in English, and they can easily be remembered by the acronym FANBOYS: for, and, nor, but, or, yet, and so. In this case, we have two clauses ("She tried on several pairs", "and she chose a blue and grey pair to replace her old shoes"), connected with a conjunction "and".