Final answer:
The phrase 'The $1 million I won in the lottery is pretty nice' is an example of understatement because it downplays the importance of winning a large sum of money.
Step-by-step explanation:
The phrase that is an example of understatement is D. The $1 million I won in the lottery is pretty nice. Understatement is a figure of speech in which a writer or speaker deliberately makes a situation seem less important or serious than it is. The example provided minimalizes the significance of winning a large sum of money by describing it as 'pretty nice', which does not capture the typical excitement and life-changing impact of such a win.