The correct answer is D.
Gatsby's mansion is described as enormous and luxurious, but is, in a way, of bad taste.
The ostentatiouness of the house reflects that Gatsby is what is known as "new money," a person that does not come from inherited money, but has rather acquired it through hard work.
Gatsby seeks to impress people (mainly Daisy) with his gigantic and conspicuous mansion, to show how much of a rich man he is now.