Input: Read this: On tracks that London Underground share with National Rail third-rail stock (the Bakerloo and District lines both have such sections), the centre rail is connected to the running rails, allowing both types of train to operate, at a compromise voltage of 660 V. Underground trains pass from one section to the other at speed; lineside electrical connections and resistances separate the two types of supply. These routes were originally solely electrified on the four-rail system by the LNWR before National Rail trains were rewired to their standard three-rail system to simplify rolling stock use.
Question: Why some sections of Bakerloo and District lines were rewired to three-rail system?

Output: to simplify rolling stock use


Input: Read this: The Korean War was a conflict between the United States and its United Nations allies and the communist powers under influence of the Soviet Union (also a UN member nation) and the People's Republic of China (which later also gained UN membership). The principal combatants were North and South Korea. Principal allies of South Korea included the United States, Canada, Australia, the United Kingdom, although many other nations sent troops under the aegis of the United Nations. Allies of North Korea included the People's Republic of China, which supplied military forces, and the Soviet Union, which supplied combat advisors and aircraft pilots, as well as arms, for the Chinese and North Korean troops.
Question:  What country was the principal ally of North Korea during the war?

Output: unanswerable


Input: Read this: Libraries and museums have been established for other presidents, but they are not part of the NARA presidential library system, and are operated by private foundations, historical societies, or state governments, including the Abraham Lincoln, Rutherford B. Hayes, William McKinley, Woodrow Wilson and Calvin Coolidge libraries. For example, the Abraham Lincoln Presidential Library and Museum is owned and operated by the state of Illinois.
Question: What state was Abraham Lincoln from?

Output: unanswerable


Input: Read this: It was during this decade that vocal house became firmly established, both in the underground and as part of the pop market, and labels such as Defected Records, Roule and Om were at the forefront of championing the emerging sound. In the mid-2000s, fusion genres such as electro house and fidget house emerged.[citation needed] This fusion is apparent in the crossover of musical styles by artists such as Dennis Ferrer and Booka Shade, with the former's production style having evolved from the New York soulful house scene and the latter's roots in techno.
Question: In what time period did Shade genres of house emerge?

Output:
unanswerable