In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

[Q]: What needs consistency?, Context: The simplest valve gears give events of fixed length during the engine cycle and often make the engine rotate in only one direction. Most however have a reversing mechanism which additionally can provide means for saving steam as speed and momentum are gained by gradually "shortening the cutoff" or rather, shortening the admission event; this in turn proportionately lengthens the expansion period. However, as one and the same valve usually controls both steam flows, a short cutoff at admission adversely affects the exhaust and compression periods which should ideally always be kept fairly constant; if the exhaust event is too brief, the totality of the exhaust steam cannot evacuate the cylinder, choking it and giving excessive compression ("kick back").[citation needed]
[A]: exhaust and compression periods


[Q]: Although Montana is a large state, it has a low what?, Context: Montana i/mɒnˈtænə/ is a state in the Western region of the United States. The state's name is derived from the Spanish word montaña (mountain). Montana has several nicknames, although none official, including "Big Sky Country" and "The Treasure State", and slogans that include "Land of the Shining Mountains" and more recently "The Last Best Place". Montana is ranked 4th in size, but 44th in population and 48th in population density of the 50 United States. The western third of Montana contains numerous mountain ranges. Smaller island ranges are found throughout the state. In total, 77 named ranges are part of the Rocky Mountains.
[A]: population


[Q]: Why did this person become famous?, Context: Chris Daughtry's performance of Fuel's "Hemorrhage (In My Hands)" on the show was widely praised and led to an invitation to join the band as Fuel's new lead singer, an invitation he declined. His performance of Live's version of "I Walk the Line" was well received by the judges but later criticized in some quarters for not crediting the arrangement to Live. He was eliminated at the top four in a shocking result.
[A]:
performance of Fuel's "Hemorrhage (In My Hands)"