Answer:
D. use the same grammatical pattern.
Step-by-step explanation:
Parallelism literally means using the same structure in (say) writing. Another way to put it, is that; when presenting a point, the sub-points must follow the same grammatical pattern or structure.
For example, the writer can choose to present the points using past tense. If by chance, there is a mix of tenses; then, the sub-points are not in parallel
This also include using phrases or sentences of identical and similar structure in each point and/or sub-points.
Option (a) to (c) refer to the layout of the sub-points. The only options that answers the question is (d).