Having parallel structure means
building sentences that are the exact same length
creating sentences that have the same tone
using the same verb tense throughout a sentence
writing two different texts at the same time

The correct answer is C. Using the same verb tense throughout a sentence

Explanation:

Parallel structures refer to structures that include the same grammatical pattern this implies using the same verb tense or the same grammatical form. For example the sentence "Susan and Same like playing chess, going to the park, and skating in the park" has a parallel structure because in this sentence the elements "playing chess", "going to the park", and "skating in the park" have the same structure as they include an -ing verb and a complement. Thus, having a parallel structure means using the same verb tense through a sentence or the same pattern.

i would say a because the main idea is what the author is the point the author is trying to get across.