Moderate means D- to take on a serious mode.
The writer used the word 'moderate' to make a comparison between those people who would lead a serious life without any excess with the group of people who would do whatever they wanted to fight against the Black Death.
What was a great movie? - It.
Just ask this question and you can easily find the subject of a sentence. Here, it is the pronoun <u>it.</u>
Answer is A. complete sentence