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

Answer: exhaust and compression periods


Question: What is the name of the discipline of the person Gregory of Tours reads?, Context: Even as the Western Roman empire collapsed, literate men acknowledged that Virgil was a master poet. Gregory of Tours read Virgil, whom he quotes in several places, along with some other Latin poets, though he cautions that "we ought not to relate their lying fables, lest we fall under sentence of eternal death."

Answer: poet


Question: How does this manifest?, Context: In their theoretical rules, the Cubist architects expressed the requirement of dynamism, which would surmount the matter and calm contained in it, through a creative idea, so that the result would evoke feelings of dynamism and expressive plasticity in the viewer. This should be achieved by shapes derived from pyramids, cubes and prisms, by arrangements and compositions of oblique surfaces, mainly triangular, sculpted facades in protruding crystal-like units, reminiscent of the so-called diamond cut, or even cavernous that are reminiscent of the late Gothic architecture. In this way, the entire surfaces of the facades including even the gables and dormers are sculpted. The grilles as well as other architectural ornaments attain a three-dimensional form. Thus, new forms of windows and doors were also created, e. g. hexagonal windows. Czech Cubist architects also designed Cubist furniture.

Answer:
shapes derived from pyramids, cubes and prisms