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An early advantage of AC is that the power-wasting resistors used in DC locomotives for speed control were not needed in an AC locomotive: multiple taps on the transformer can supply a range of voltages. Separate low-voltage transformer windings supply lighting and the motors driving auxiliary machinery. More recently, the development of very high power semiconductors has caused the classic "universal" AC/DC motor to be largely replaced with the three-phase induction motor fed by a variable frequency drive, a special inverter that varies both frequency and voltage to control motor speed. These drives can run equally well on DC or AC of any frequency, and many modern electric locomotives are designed to handle different supply voltages and frequencies to simplify cross-border operation.
What will AC/DC motor be replaced with?
A: three-phase induction motor

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The Canadian constitution determines that the Commander-in-Chief of the Canadian Armed Forces is the country's sovereign, who, since 1904, has authorized his or her viceroy, the governor general, to exercise the duties ascribed to the post of Commander-in-Chief and to hold the associated title since 1905. All troop deployment and disposition orders, including declarations of war, fall within the royal prerogative and are issued as Orders in Council, which must be signed by either the monarch or governor general. Under the Westminster system's parliamentary customs and practices, however, the monarch and viceroy must generally follow the advice of his or her ministers in Cabinet, including the prime minister and minister of national defence, who are accountable to the elected House of Commons.
Who's advice is the monarch supposed to follow regarding these orders?
A: the advice of his or her ministers in Cabinet

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Though they have not had the level of exposure as other wrestlers, bears have long been a part of professional wrestling. Usually declawed and muzzled, they often wrestled shoot matches against audience members, offered a cash reward if they could pin the bear. They also wrestled professionals in worked, often battle royal or handicap, matches (usually booked so the bear won). Though they have wrestled around the world and continue to do so, wrestling bears enjoyed their greatest popularity in the Southern United States, during the 1960s and 1970s. The practice of bear wrestling has met strong opposition from animal rights activists in recent decades, contributing to its lack of mainstream acceptance. As of 2006, it is banned in 20 U.S. states. Perhaps the most famous wrestling bears are Ginger, Victor, Hercules and Terrible Ted.
How many states have banned bear wrestling as of 2006?
A: 20

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The first amniotes apparently arose in the Late Carboniferous. They descended from earlier reptiliomorph amphibious tetrapods, which lived on land that was already inhabited by insects and other invertebrates as well as by ferns, mosses and other plants. Within a few million years, two important amniote lineages became distinct: the synapsids, which would later include the common ancestor of the mammals; and the sauropsids, which would eventually come to include turtles, lizards, snakes, crocodilians, dinosaurs and birds. Synapsids have a single hole (temporal fenestra) low on each side of the skull.
When did amphibious tetrapods become prominent?
A:
unanswerable