Problem: Middle Ages:

The invasions brought new ethnic groups to Europe, although some regions received a larger influx of new peoples than others. In Gaul for instance, the invaders settled much more extensively in the north-east than in the south-west. Slavic peoples settled in Central and Eastern Europe and the Balkan Peninsula. The settlement of peoples was accompanied by changes in languages. The Latin of the Western Roman Empire was gradually replaced by languages based on, but distinct from, Latin, collectively known as Romance languages. These changes from Latin to the new languages took many centuries. Greek remained the language of the Byzantine Empire, but the migrations of the Slavs added Slavonic languages to Eastern Europe.

What is the collective name for languages derived from Latin?
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A: Romance languages

Problem: The Japanese defenders recognized the possibility of a renewed invasion, and began construction of a great stone barrier around Hakata Bay in 1276. Completed in 1277, this wall stretched for 20 kilometers around the border of the bay. This would later serve as a strong defensive point against the Mongols. The Mongols attempted to settle matters in a diplomatic way from 1275 to 1279, but every envoy sent to Japan was executed. This set the stage for one of the most famous engagements in Japanese history.
How long was the Hakata Bay barrier?
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Answer: 20 kilometers

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Dog behavior is the internally coordinated responses (actions or inactions) of the domestic dog (individuals or groups) to internal and/or external stimuli. As the oldest domesticated species, with estimates ranging from 9,00030,000 years BCE, the minds of dogs inevitably have been shaped by millennia of contact with humans. As a result of this physical and social evolution, dogs, more than any other species, have acquired the ability to understand and communicate with humans and they are uniquely attuned to our behaviors. Behavioral scientists have uncovered a surprising set of social-cognitive abilities in the otherwise humble domestic dog. These abilities are not possessed by the dog's closest canine relatives nor by other highly intelligent mammals such as great apes. Rather, these skills parallel some of the social-cognitive skills of human children.
More than any other species, dogs are able to do what with people?
A: understand and communicate

Context and question: Contract law covers obligations established by agreement (express or implied) between private parties. Generally, contract law in transactions involving the sale of goods has become highly standardized nationwide as a result of the widespread adoption of the Uniform Commercial Code. However, there is still significant diversity in the interpretation of other kinds of contracts, depending upon the extent to which a given state has codified its common law of contracts or adopted portions of the Restatement (Second) of Contracts.
What kinds of agreements do contract law cover?
Answer: express or implied

Question: Controversy persists over whether the Rus' were Varangians (Vikings) or Slavs. This uncertainty is due largely to a paucity of contemporary sources. Attempts to address this question instead rely on archaeological evidence, the accounts of foreign observers, legends and literature from centuries later. To some extent the controversy is related to the foundation myths of modern states in the region. According to the "Normanist" view, the Rus' were Scandinavians, while Russian and Ukrainian nationalist historians generally argue that the Rus' were themselves Slavs. Normanist theories focus on the earliest written source for the East Slavs, the Russian Primary Chronicle, although even this account was not produced until the 12th century. Nationalist accounts have suggested that the Rus' were present before the arrival of the Varangians, noting that only a handful of Scandinavian words can be found in modern Russian and that Scandinavian names in the early chronicles were soon replaced by Slavic names. Nevertheless, archaeological evidence from the area suggests that a Scandinavian population was present during the 10th century at the latest. On balance, it seems likely that the Rus' proper were a small minority of Scandinavians who formed an elite ruling class, while the great majority of their subjects were Slavs. Considering the linguistic arguments mounted by nationalist scholars, if the proto-Rus' were Scandinavians, they must have quickly become nativized, adopting Slavic languages and other cultural practices.
Is there an answer to this question: What did the Russian believe the Rus were not?

Answer: unanswerable

A new style of wafers composed of gallium-nitride-on-silicon (GaN-on-Si) is being used to produce white LEDs using 200-mm silicon wafers. This avoids the typical costly sapphire substrate in relatively small 100- or 150-mm wafer sizes. The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted. It is predicted that by 2020, 40% of all GaN LEDs will be made with GaN-on-Si. Manufacturing large sapphire material is difficult, while large silicon material is cheaper and more abundant. LED companies shifting from using sapphire to silicon should be a minimal investment.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What needs to not be used to reflect light that would otherwise be wasted?
Ah, so..
unanswerable