This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.

[Q]: Passage: Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used for this purpose, and this is likely to remain one of their major uses until the price drops low enough to make signaling and illumination uses more widespread. Barcode scanners are the most common example of machine vision, and many low cost products use red LEDs instead of lasers. Optical computer mice are an example of LEDs in machine vision, as it is used to provide an even light source on the surface for the miniature camera within the mouse. LEDs constitute a nearly ideal light source for machine vision systems for several reasons:
[A]: non-LEDs are often used for what type of systems?

[Q]: Passage: In 1872, Russian Alexander Lodygin invented an incandescent light bulb and obtained a Russian patent in 1874. He used as a burner two carbon rods of diminished section in a glass receiver, hermetically sealed, and filled with nitrogen, electrically arranged so that the current could be passed to the second carbon when the first had been consumed. Later he lived in the USA, changed his name to Alexander de Lodyguine and applied and obtained patents for incandescent lamps having chromium, iridium, rhodium, ruthenium, osmium, molybdenum and tungsten filaments, and a bulb using a molybdenum filament was demonstrated at the world fair of 1900 in Paris.
[A]: Who did not patent an incandescent light bulb in 1872?

[Q]: Passage: On 17 March 1883, she fell down some stairs at Windsor, which left her lame until July; she never fully recovered and was plagued with rheumatism thereafter. Brown died 10 days after her accident, and to the consternation of her private secretary, Sir Henry Ponsonby, Victoria began work on a eulogistic biography of Brown. Ponsonby and Randall Davidson, Dean of Windsor, who had both seen early drafts, advised Victoria against publication, on the grounds that it would stoke the rumours of a love affair. The manuscript was destroyed. In early 1884, Victoria did publish More Leaves from a Journal of a Life in the Highlands, a sequel to her earlier book, which she dedicated to her "devoted personal attendant and faithful friend John Brown". On the day after the first anniversary of Brown's death, Victoria was informed by telegram that her youngest son, Leopold, had died in Cannes. He was "the dearest of my dear sons", she lamented. The following month, Victoria's youngest child, Beatrice, met and fell in love with Prince Henry of Battenberg at the wedding of Victoria's granddaughter Princess Victoria of Hesse and by Rhine to Henry's brother Prince Louis of Battenberg. Beatrice and Henry planned to marry, but Victoria opposed the match at first, wishing to keep Beatrice at home to act as her companion. After a year, she was won around to the marriage by Henry and Beatrice's promise to remain living with and attending her.
[A]:
What year didn't Victoria fall down the stairs at Windsor?