This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

[Q]: Passage: Reflections generally affect polarization. For radio waves, one important reflector is the ionosphere which can change the wave's polarization. Thus for signals received following reflection by the ionosphere (a skywave), a consistent polarization cannot be expected. For line-of-sight communications or ground wave propagation, horizontally or vertically polarized transmissions generally remain in about the same polarization state at the receiving location. Matching the receiving antenna's polarization to that of the transmitter can make a very substantial difference in received signal strength. Question: What reflector can change the waves polarization?
[A]: ionosphere


[Q]: Passage: The Cathedral of Brasília in the capital of the Federative Republic of Brazil, is an expression of the architect Oscar Niemeyer. This concrete-framed hyperboloid structure, seems with its glass roof reaching up, open, to the heavens. On 31 May 1970, the Cathedral’s structure was finished, and only the 70 m (229.66 ft) diameter of the circular area were visible. Niemeyer's project of Cathedral of Brasília is based in the hyperboloid of revolution which sections are asymmetric. The hyperboloid structure itself is a result of 16 identical assembled concrete columns. These columns, having hyperbolic section and weighing 90 t, represent two hands moving upwards to heaven. The Cathedral was dedicated on 31 May 1970. Question: When was the Cathedral of Brasília dedicated?
[A]: 31 May 1970


[Q]: Passage: The 17th century Royal Ujazdów Castle currently houses Centre for Contemporary Art, with some permanent and temporary exhibitions, concerts, shows and creative workshops. The Centre currently realizes about 500 projects a year. Zachęta National Gallery of Art, the oldest exhibition site in Warsaw, with a tradition stretching back to the mid-19th century organises exhibitions of modern art by Polish and international artists and promotes art in many other ways. Since 2011 Warsaw Gallery Weekend is held on last weekend of September. Question: When is the Warsaw Gallery Weekend held?
[A]:
last weekend of September