With nearly a third of Bostonians using public transit for their commute to work, Boston has the fifth-highest rate of public transit usage in the country. Boston's subway system, the Massachusetts Bay Transportation Authority (MBTA—known as the "T") operates the oldest underground rapid transit system in the Americas, and is the fourth-busiest rapid transit system in the country, with 65.5 miles (105 km) of track on four lines. The MBTA also operates busy bus and commuter rail networks, and water shuttles.
Where does Boston rank nationally in terms of public transportation use?
fifth-highest

Estonian (eesti keel [ˈeːsti ˈkeːl] ( listen)) is the official language of Estonia, spoken natively by about 1.1 million people in Estonia and tens of thousands in various migrant communities. It belongs to the Finnic branch of the Uralic language family.
How many people in different migrant communities speak Estonian?
tens of thousands

There is little consensus on the precise beginning of the Age of Enlightenment; the beginning of the 18th century (1701) or the middle of the 17th century (1650) are often used as epochs. French historians usually place the period, called the Siècle des Lumières (Century of Enlightenments), between 1715 and 1789, from the beginning of the reign of Louis XV until the French Revolution. If taken back to the mid-17th century, the Enlightenment would trace its origins to Descartes' Discourse on Method, published in 1637. In France, many cited the publication of Isaac Newton's Principia Mathematica in 1687. It is argued by several historians and philosophers that the beginning of the Enlightenment is when Descartes shifted the epistemological basis from external authority to internal certainty by his cogito ergo sum published in 1637. As to its end, most scholars use the last years of the century, often choosing the French Revolution of 1789 or the beginning of the Napoleonic Wars (1804–15) as a convenient point in time with which to date the end of the Enlightenment.
In what year was Issaac Newton's Principia Mathematica published?
1687