question:  Marion is approximately 50 mi north of a city that is the third-most populous what in the U.S.?
answer: state capital
context: Title: Columbus, Ohio
  Passage: Columbus ( ) is the capital and largest city of the U.S. state of Ohio.  It is the 14th-largest city in the United States, with a population of 860,090 as of 2016 estimates.  This makes Columbus the third-most populous state capital in the United States, and the second-largest city in the Midwestern United States, after Chicago.  It is the core city of the Columbus, Ohio, Metropolitan Statistical Area, which encompasses ten counties.  With a population of 2,021,632, it is Ohio's third-largest metropolitan area.
  Title: Marion, Ohio
  Passage: Marion is a city in and the county seat of Marion County, Ohio, United States.  The municipality is located in north-central Ohio, approximately 50 mi north of Columbus.
  Title: Knox County, Tennessee
  Passage: Knox County is a county in the U.S. state of Tennessee.  As of the 2010 census, the population was 432,226, making it the third-most populous county in Tennessee.  Its county seat is Knoxville, the third-most populous city in Tennessee.
  Title: Santa Fe de Antioquia
  Passage: Santa Fe de Antioquia is a municipality in the Antioquia Department, Colombia.  The city is located approximately 50 mi north of Medellín, the department capital.  It has a population of approximately 23,000 inhabitants.
  Title: Blue Flint Ethanol
  Passage: Blue Flint Ethanol is an bioethanol producing company and a production plant with a same name, located in Underwood, North Dakota approximately 50 mi north of Bismarck.  The plant is unique in the fact that rather than burning fuels, such as coal or natural gas to drive the production process, waste heat from electrical generation at the Coal Creek Station is used.  The US$100 million plant is capable of processing 18 million bushels (460,000 metric tons) of corn to produce 50 million gallons (190 million liters) of ethanol each year, and is estimated to have a net annual economic impact of $160 million on the North Dakota economy, as well as the creation of approximately 40 new jobs to run the plant.  In addition to producing ethanol the plant will also produce dry distillers grains, a byproduct of the distillation process which is used as animal feed.  Of the 18 million bushels of corn used each year for feedstock, the majority will be grown in southeast North Dakota and brought in via rail, with the remaining one third being produced locally.  In 2006 the Blue Flint Ethanol project was awarded the Project of the Year Award by Governor John Hoeven.
  Title: Demographics of Mexico
  Passage: With a population of over 123 million in 2017, Mexico ranks as the 10th most populated country in the world.  It is the most populous Spanish-speaking country and the third-most populous in the Americas after United States and Brazil.  Throughout most of the twentieth century Mexico's population was characterized by rapid growth.  Although this tendency has been reversed and average annual population growth over the last five years was less than 1%, the demographic transition is still in progress, and Mexico still has a large cohort of youths.  The most populous city in the country is the capital, Mexico City, with a population of 8.9 million (2016), and its metropolitan area is also the most populated with 20.1 million (2010).  Approximately 50% of the population lives in one of the 55 large metropolitan areas in the country.  In total, about 78.84% of the population of the country lives in urban areas, meaning that only 21.16% live in rural areas.
  Title: Cambridge
  Passage: Cambridge ( ) is a university city and the county town of Cambridgeshire, England, on the River Cam approximately 50 mi north of London.  At the United Kingdom Census 2011, its population was 123,867, including 24,488 students.
citations: Marion, Ohio Columbus, Ohio