Answer:
Hi there! It looks like you forgot to upload the questions that this question is based on. Because of that, I'm not able to directly answer your question.
Parallel structure is the concept of having the same grammatical structure within one or multiple sentences. For example, saying "I am running, swim, and ate" is not appropriate use of parallel structure because the verbs are inconsistent with the tenses used. And as for the comma, make sure you use it to separate items in a series (of 3 or more), and for attaching thoughts onto a sentence (such as the first part of this sentence).\
Hope this helped a little!