The sentence that uses parallel structures is B) My three favorite activities are writing, reading, and going to the library. A parallel structure means that the same form of a verb is used in a sentence, and as you can see, here only gerunds are used - writing, reading, going - they all have -ing in the end. The other sentences don't have a parallel structure because they don't use the same forms.
Monarchies will dominate society, trade and economic opportunities, and in consequence, political institutions will become weaker and the economy will decline.
