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At extremely large airports, a circuit is in place but not usually used. Rather, aircraft (usually only commercial with long routes) request approach clearance while they are still hours away from the airport, often before they even take off from their departure point. Large airports have a frequency called Clearance Delivery which is used by departing aircraft specifically for this purpose. This then allows aircraft to take the most direct approach path to the runway and land without worrying about interference from other aircraft. While this system keeps the airspace free and is simpler for pilots, it requires detailed knowledge of how aircraft are planning to use the airport ahead of time and is therefore only possible with large commercial airliners on pre-scheduled flights. The system has recently become so advanced that controllers can predict whether an aircraft will be delayed on landing before it even takes off; that aircraft can then be delayed on the ground, rather than wasting expensive fuel waiting in the air.
At an extremely large airport, what is in place but not usually used?
A: a circuit

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Most of the English colonists had arrived as indentured servants, hiring themselves out as laborers for a fixed period to pay for their passage. In the early years the line between indentured servants and African slaves or laborers was fluid. Some Africans were allowed to earn their freedom before slavery became a lifelong status. Most of the free colored families formed in North Carolina before the Revolution were descended from unions or marriages between free white women and enslaved or free African or African-American men. Because the mothers were free, their children were born free. Many had migrated or were descendants of migrants from colonial Virginia. As the flow of indentured laborers to the colony decreased with improving economic conditions in Great Britain, planters imported more slaves, and the state's legal delineations between free and slave status tightened, effectively hardening the latter into a racial caste. The economy's growth and prosperity was based on slave labor, devoted first to the production of tobacco.
As indentured servants improved the economy, there became a greater need to import more what?
A: slaves

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Houston is the seat of the internationally renowned Texas Medical Center, which contains the world's largest concentration of research and healthcare institutions. All 49 member institutions of the Texas Medical Center are non-profit organizations. They provide patient and preventive care, research, education, and local, national, and international community well-being. Employing more than 73,600 people, institutions at the medical center include 13 hospitals and two specialty institutions, two medical schools, four nursing schools, and schools of dentistry, public health, pharmacy, and virtually all health-related careers. It is where one of the first—and still the largest—air emergency service, Life Flight, was created, and a very successful inter-institutional transplant program was developed. More heart surgeries are performed at the Texas Medical Center than anywhere else in the world.
How many non profit organizations are members of the Medical Center?
A: 49

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On 9 March 2016, The Sun's front page proclaimed that Queen Elizabeth II was backing "Brexit", a common term for a British withdrawal from the European Union. It claimed that in 2011 at Windsor Castle, while having lunch with Deputy Prime Minister Nick Clegg, the monarch criticised the union. Clegg denied that the Queen made such a statement, and a Buckingham Palace spokesperson confirmed that a complaint had been made to the Independent Press Standards Organisation over a breach of guidelines relating to accuracy.
Who refuted the statement that the Queen was critical of the European Union?
A:
Deputy Prime Minister Nick Clegg