Input: Read this: The iconic New York City Subway system is the largest rapid transit system in the world when measured by stations in operation, with 469, and by length of routes. New York's subway is notable for nearly the entire system remaining open 24 hours a day, in contrast to the overnight shutdown common to systems in most cities, including Hong Kong, London, Paris, Seoul, and Tokyo. The New York City Subway is also the busiest metropolitan rail transit system in the Western Hemisphere, with 1.75 billion passengers rides in 2014, while Grand Central Terminal, also popularly referred to as "Grand Central Station", is the world's largest railway station by number of train platforms.
Question: Which subway system is considered the largest in the world?

Output: New York City Subway system


Input: Read this: The Quine-Duhem thesis argues that it's impossible to test a single hypothesis on its own, since each one comes as part of an environment of theories. Thus we can only say that the whole package of relevant theories has been collectively falsified, but cannot conclusively say which element of the package must be replaced. An example of this is given by the discovery of the planet Neptune: when the motion of Uranus was found not to match the predictions of Newton's laws, the theory "There are seven planets in the solar system" was rejected, and not Newton's laws themselves. Popper discussed this critique of naïve falsificationism in Chapters 3 and 4 of The Logic of Scientific Discovery. For Popper, theories are accepted or rejected via a sort of selection process. Theories that say more about the way things appear are to be preferred over those that do not; the more generally applicable a theory is, the greater its value. Thus Newton's laws, with their wide general application, are to be preferred over the much more specific "the solar system has seven planets".[dubious – discuss]
Question: What thesis says it is possible to test a single hypothesis alone?

Output: unanswerable


Input: Read this: Japan and Germany are great powers too, though due to their large advanced economies (having the third and fourth largest economies respectively) rather than their strategic and hard power capabilities (i.e., the lack of permanent seats and veto power on the UN Security Council or strategic military reach). Germany has been a member together with the five permanent Security Council members in the P5+1 grouping of world powers. Like China, France, Russia and the United Kingdom; Germany and Japan have also been referred to as middle powers.
Question: What benefits do middle power countries have as permanent members at the UN?

Output: unanswerable


Input: Read this: Subsequently, in October 2001, U.S. forces (with UK and coalition allies) invaded Afghanistan to oust the Taliban regime. On 7 October 2001, the official invasion began with British and U.S. forces conducting airstrike campaigns over enemy targets. Kabul, the capital city of Afghanistan, fell by mid-November. The remaining al-Qaeda and Taliban remnants fell back to the rugged mountains of eastern Afghanistan, mainly Tora Bora. In December, Coalition forces (the U.S. and its allies) fought within that region. It is believed that Osama bin Laden escaped into Pakistan during the battle.
Question: When did Afghanistan forces invade the UK?

Output:
unanswerable