Mushrooms

most americans are familiar with the mushrooms they eat on a pizza or in a salad. but most people do not know that more than 3,000 different types of mushrooms are grown around the world. some mushrooms are less than an inch high, while others are more than 15 inches tall. they have strange names like shiitake, portobello and black trumpet . until world war ii, most mushrooms were grown in asia, where they were used in soups and vegetable dishes. but today, the united states is the world’s largest supplier of mushrooms. from 1986 to 1999, worldwide mushroom production grew from 470 million pounds to 860 million pounds.

what role does the underlined sentence play in this paragraph?

it is a statistic that serves as a supporting detail.
it is an example that serves as a supporting detail.
it is the topic sentence.
it is a fact that serves as a supporting detail.