The colors in her art project included splotches of brown, patches where it was yellow, and green streaks everywhere. This is a parallel.
Our favorite pastimes are spending time at the library, to ride around through the countryside, and huge banana splits to share. This is not parallel
That tribe of Native Americans was famous for weaving rugs, shaping pottery, and designing turquoise jewelry. This is parallel
Parallel structure means that the items included in a list must be in the same form, in the first case there are nouns and in the third case the list is on gerunds
Usually the reason is D. It can make us biased, I don't see any other option making sense
