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.

Passage: The preludes, many of which are very brief (some consisting of simple statements and developments of a single theme or figure), were described by Schumann as "the beginnings of studies". Inspired by J.S. Bach's The Well-Tempered Clavier, Chopin's preludes move up the circle of fifths (rather than Bach's chromatic scale sequence) to create a prelude in each major and minor tonality. The preludes were perhaps not intended to be played as a group, and may even have been used by him and later pianists as generic preludes to others of his pieces, or even to music by other composers, as Kenneth Hamilton suggests: he has noted a recording by Ferruccio Busoni of 1922, in which the Prelude Op. 28 No. 7 is followed by the Etude Op. 10 No. 5. Question: What piece of Bach's did Chopin take inspiration for his preludes?
The Well-Tempered Clavier

Passage: Prior to Confederation in 1867, residents of the colonies in what is now Canada served as regular members of French and British forces and in local militia groups. The latter aided in the defence of their respective territories against attacks by other European powers, Aboriginal peoples, and later American forces during the American Revolutionary War and War of 1812, as well as in the Fenian raids, Red River Rebellion, and North-West Rebellion. Consequently, the lineages of some Canadian army units stretch back to the early 19th century, when militia units were formed to assist in the defence of British North America against invasion by the United States. Question: The forces of what countries did people serve before the unification?
French and British forces

Passage: The Gregorian calendar improves the approximation made by the Julian calendar by skipping three Julian leap days in every 400 years, giving an average year of 365.2425 mean solar days long. This approximation has an error of about one day per 3,300 years with respect to the mean tropical year. However, because of the precession of the equinoxes, the error with respect to the vernal equinox (which occurs, on average, 365.24237 days apart near 2000) is 1 day every 7,700 years, assuming a constant time interval between vernal equinoxes, which is not true. By any criterion, the Gregorian calendar is substantially more accurate than the 1 day in 128 years error of the Julian calendar (average year 365.25 days). Question: How many days must be skipped to align the calendar with mean solar days in a year?
three Julian leap days