Gerunds are words that end in -ing but are mainly used as nouns. In the given sentence, "Swimming against the current is just one of the challenging aspects of people participating in the triathlon will be facing", the gerund in the sentence is the word 'swimming'.
I'd say D because it says "if they ever should use it in earnest against each other, it will surely split." Government only has as much power as the people let it have
