The most accurate statement about modern Buddhism from the options provided is:
More than two million Buddhists live in the United States.
While there are also significant Buddhist populations in Asia and other parts of the world, the statement about the U.S. population aligns with estimates of the number of Buddhists in the country. The other statements either contain inaccuracies or are misleading. For example, Buddhism's presence in India is limited compared to its historical significance, and most Buddhists do not live in monasteries.