Abstract nouns characterize qualities and ideas, rather than material objects.
Concrete nouns - Rainbow, coffee, dog.
Abstract nouns - Freedom, anger, democracy.
The main difference is that we can perceive concrete nouns with our senses, while we cannot perceive abstract nouns with our senses.
The abstract noun in this sentence is...
Answer:
Loyalty.
June, 1863 saw French troops reach Mexico and cause the current government officials to flee.
Obviously it about sustaining equality. The excerpt is talking about how diversity is a problem, well equality is a way of trying to solve that problem.
I'd say that D is the right answer.