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 is Rayleigh scattering?, Context: In nature, the red color of blood comes from hemoglobin, the iron-containing protein found in the red blood cells of all vertebrates. The red color of the Grand Canyon and other geological features is caused by hematite or red ochre, both forms of iron oxide. It also causes the red color of the planet Mars. The red sky at sunset and sunrise is caused by an optical effect known as Rayleigh scattering, which, when the sun is low or below the horizon, increases the red-wavelength light that reaches the eye. The color of autumn leaves is caused by pigments called anthocyanins, which are produced towards the end of summer, when the green chlorophyll is no longer produced. One to two percent of the human population has red hair; the color is produced by high levels of the reddish pigment pheomelanin (which also accounts for the red color of the lips) and relatively low levels of the dark pigment eumelanin.

Answer: optical effect

Question: who avenged Chu'Tsai's forefathers?, Context: Genghis Khan realised that he needed people who could govern cities and states conquered by him. He also realised that such administrators could not be found among his Mongol people because they were nomads and thus had no experience governing cities. For this purpose Genghis Khan invited a Khitan prince, Chu'Tsai, who worked for the Jin and had been captured by the Mongol army after the Jin dynasty was defeated. Jin had captured power by displacing Khitan. Genghis told Chu'Tsai, who was a lineal descendant of Khitan rulers, that he had avenged Chu'Tsai's forefathers. Chu'Tsai responded that his father served the Jin dynasty honestly and so did he; also he did not consider his own father his enemy, so the question of revenge did not apply. This reply impressed Genghis Khan. Chu'Tsai administered parts of the Mongol Empire and became a confidant of the successive Mongol Khans.

Answer: Genghis Khan

Question: What did the language spoken in the centre of of the Low German area become?, Context: Three Germanic dialects were originally spoken in the Low Countries: Frisian in the north and along the western coast; Saxon in the east (contiguous with the Low German area); and Franconian in the centre and south. It is the Franconian dialects that is designated as Old Dutch, and that would develop in Middle Dutch and later Modern Dutch. The division in these development phases is mostly conventional, since the transition between them was very gradual. One of the few moments linguists can detect somewhat of a revolution is when the Dutch standard language emerged and quickly established itself. The development of the Dutch language is illustrated by the following sentence in Old, Middle and Modern Dutch:

Answer:
Middle Dutch and later Modern Dutch