instruction:
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.
question:
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]
answer:
What time cycle did studies in 1938 and 1990s use on humans?


question:
By about 1910,[note 1] bound collections of empty sleeves with a paperboard or leather cover, similar to a photograph album, were sold as record albums that customers could use to store their records (the term "record album" was printed on some covers). These albums came in both 10-inch and 12-inch sizes. The covers of these bound books were wider and taller than the records inside, allowing the record album to be placed on a shelf upright, like a book, suspending the fragile records above the shelf and protecting them.
answer:
When could record album covers first be found?


question:
In July 2013, there were 41,000 non-Germans by citizenship living in Thuringia (1.9% of the population − among the smallest proportions of any state in Germany). Nevertheless, the number rose from 33,000 in July 2011, an increase of 24% in only two years. About 4% of the population are migrants (including persons that already received the German citizenship). The biggest groups of foreigners by citizenship are (as of 2012): Russians (3,100), Poles (3,000), Vietnamese (2,800), Turks (2,100) and Ukrainians (2,000). The amount of foreigners varies between regions: the college towns Erfurt, Jena, Weimar and Ilmenau have the highest rates, whereas there are almost no migrants living in the most rural smaller municipalities.
answer:
How many non-Germans lived in Thuringia in 2013?