Q: This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
Passage: The capital is Nashville, though Knoxville, Kingston, and Murfreesboro have all served as state capitals in the past. Memphis has the largest population of any city in the state. Nashville's 13-county metropolitan area has been the state's largest since c. 1990. Chattanooga and Knoxville, both in the eastern part of the state near the Great Smoky Mountains, each has approximately one-third of the population of Memphis or Nashville. The city of Clarksville is a fifth significant population center, some 45 miles (72 km) northwest of Nashville. Murfreesboro is the sixth-largest city in Tennessee, consisting of some 108,755 residents. Question: How many counties are part of Nashville's metropolitan area?
A:
13