Problem: Circadian rhythm:

The rhythm is linked to the lightdark cycle. Animals, including humans, kept in total darkness for extended periods eventually function with a free-running rhythm. Their sleep cycle is pushed back or forward each "day", depending on whether their "day", their endogenous period, is shorter or longer than 24 hours. The environmental cues that reset the rhythms each day are called zeitgebers (from the German, "time-givers"). Totally blind subterranean mammals (e.g., blind mole rat Spalax sp.) are able to maintain their endogenous clocks in the apparent absence of external stimuli. Although they lack image-forming eyes, their photoreceptors (which detect light) are still functional; they do surface periodically as well.[page needed]

What do blind mole rats have in place of vision?
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A: photoreceptors

Problem: Elizabeth's personal fortune has been the subject of speculation for many years. Jock Colville, who was her former private secretary and a director of her bank, Coutts, estimated her wealth in 1971 at 2 million (equivalent to about 25 million today). In 1993, Buckingham Palace called estimates of 100 million "grossly overstated". She inherited an estimated 70 million estate from her mother in 2002. The Sunday Times Rich List 2015 estimated her private wealth at 340 million, making her the 302nd richest person in the UK.
In what year did Jock Colville leave Elizabeth's service?
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Answer: unanswerable

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Nanjing, with a total land area of 6,598 square kilometres (2,548 sq mi), is situated in the heartland of drainage area of lower reaches of Yangtze River, and in Yangtze River Delta, one of the largest economic zones of China. The Yangtze River flows past the west side and then north side of Nanjing City, while the Ningzheng Ridge surrounds the north, east and south side of the city. The city is 300 kilometres (190 mi) west-northwest of Shanghai, 1,200 kilometres (750 mi) south-southeast of Beijing, and 1,400 kilometres (870 mi) east-northeast of Chongqing. The downstream Yangtze River flows from Jiujiang, Jiangxi, through Anhui and Jiangsu to East Sea, north to drainage basin of downstream Yangtze is Huai River basin and south to it is Zhe River basin, and they are connected by the Grand Canal east to Nanjing. The area around Nanjing is called Hsiajiang (, Downstream River) region, with Jianghuai () stressing northern part and Jiangzhe () stressing southern part. The region is also known as Dongnan (, South East, the Southeast) and Jiangnan (, River South, south of Yangtze).
How large is Nanjing, in miles?
A: 2,548 sq mi

Context and question: LEDs have also been used as a medium-quality voltage reference in electronic circuits. The forward voltage drop (e.g. about 1.7 V for a normal red LED) can be used instead of a Zener diode in low-voltage regulators. Red LEDs have the flattest I/V curve above the knee. Nitride-based LEDs have a fairly steep I/V curve and are useless for this purpose. Although LED forward voltage is far more current-dependent than a Zener diode, Zener diodes with breakdown voltages below 3 V are not widely available.
What LEDs have a not very steep I/V curve?
Answer: unanswerable

Question: The brain generally forms a ring round the pharynx (throat), consisting of a pair of ganglia (local control centers) above and in front of the pharynx, linked by nerve cords either side of the pharynx to another pair of ganglia just below and behind it. The brains of polychaetes are generally in the prostomium, while those of clitellates are in the peristomium or sometimes the first segment behind the peristomium. In some very mobile and active polychaetes the brain is enlarged and more complex, with visible hindbrain, midbrain and forebrain sections. The rest of the central nervous system is generally "ladder-like", consisting of a pair of nerve cords that run through the bottom part of the body and have in each segment paired ganglia linked by a transverse connection. From each segmental ganglion a branching system of local nerves runs into the body wall and then encircles the body. However, in most polychaetes the two main nerve cords are fused, and in the tube-dwelling genus Owenia the single nerve chord has no ganglia and is located in the epidermis.
Is there an answer to this question: What is a pharynx?

Answer: throat

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
In Northern Germany, Netherlands, northern Poland, Denmark, and the Baltic countries local building stone was unavailable but there was a strong tradition of building in brick. The resultant style, Brick Gothic, is called "Backsteingotik" in Germany and Scandinavia and is associated with the Hanseatic League. In Italy, stone was used for fortifications, but brick was preferred for other buildings. Because of the extensive and varied deposits of marble, many buildings were faced in marble, or were left with undecorated facade so that this might be achieved at a later date.
Why were many buildings covered with marbles?
A:
unanswerable