This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

[Q]: Studies by Nathaniel Kleitman in 1938 and by Derk-Jan Dijk and Charles Czeisler in the 1990s put human subjects on enforced 28-hour sleep–wake cycles, in constant dim light and with other time cues suppressed, for over a month. Because normal people cannot entrain to a 28-hour day in dim light if at all,[citation needed] this is referred to as a forced desynchrony protocol. Sleep and wake episodes are uncoupled from the endogenous circadian period of about 24.18 hours and researchers are allowed to assess the effects of circadian phase on aspects of sleep and wakefulness including sleep latency and other functions.[page needed]
[A]: What time cycle did studies in 1938 and 1990s use on humans?


[Q]: 48 of Switzerland's mountains are 4,000 metres (13,000 ft) above sea in altitude or higher. At 4,634 m (15,203 ft), Monte Rosa is the highest, although the Matterhorn (4,478 m or 14,692 ft) is often regarded as the most famous. Both are located within the Pennine Alps in the canton of Valais. The section of the Bernese Alps above the deep glacial Lauterbrunnen valley, containing 72 waterfalls, is well known for the Jungfrau (4,158 m or 13,642 ft) Eiger and Mönch, and the many picturesque valleys in the region. In the southeast the long Engadin Valley, encompassing the St. Moritz area in canton of Graubünden, is also well known; the highest peak in the neighbouring Bernina Alps is Piz Bernina (4,049 m or 13,284 ft).
[A]: What is the highest mountain in Switzerland?


[Q]: The High Middle Ages was a period of tremendous expansion of population. The estimated population of Europe grew from 35 to 80 million between 1000 and 1347, although the exact causes remain unclear: improved agricultural techniques, the decline of slaveholding, a more clement climate and the lack of invasion have all been suggested. As much as 90 per cent of the European population remained rural peasants. Many were no longer settled in isolated farms but had gathered into small communities, usually known as manors or villages. These peasants were often subject to noble overlords and owed them rents and other services, in a system known as manorialism. There remained a few free peasants throughout this period and beyond, with more of them in the regions of Southern Europe than in the north. The practice of assarting, or bringing new lands into production by offering incentives to the peasants who settled them, also contributed to the expansion of population.
[A]:
What was the approximate population of Europe in 1347?