Question: The capital of Danish Estonia (Danish: Hertugdømmet Estland) was Reval (Tallinn), founded at the place of Lyndanisse after the invasion of 1219. The Danes built the fortress of Castrum Danorum at Toompea Hill. Estonians still call their capital "Tallinn", which according to legend derives from Taani linna (meaning Danish town or castle). Reval was granted Lübeck city rights (1248) and joined the Hanseatic League. Even today, Danish influence can be seen in heraldic symbols. The Danish cross is on the city of Tallinn's coat of arms, and Estonia's coat of arms displays three lions similar to those found on the Danish coat of arms.
Try to answer this question if possible: What structure was built at Toompea Hill?
Answer: the fortress of Castrum Danorum
Question: In the Soviet Union, in the 1970s, a comparison was made between systems electrified at 3 kV DC and 25 kV AC (50 Hz). The results showed that percentage losses in the overhead wires (catenary and contact wires) was over 3 times greater for 3 kV DC than for 25 kV AC. But when the conversion losses were all taken into account and added to overhead wire losses (including cooling blower energy) the 25 kV AC lost a somewhat higher percent of energy than for 3 kV DC. Thus in spite of the much higher losses in the catenary, the 3 kV DC was a little more energy efficient than AC in providing energy from the USSR power grid to the terminals of the traction motors (all DC at that time). While both systems use energy in converting higher voltage AC from the USSR's power grid to lower voltage DC, the conversions for the DC system all took place (at higher efficiency) in the railway substation, while most of the conversion for the AC system took place inside the locomotive (at lower efficiency). Consider also that it takes energy to constantly move this mobile conversion hardware over the rails while the stationary hardware in the railway substation doesn't incur this energy cost. For more details see: Wiki: Soviet Union DC vs. AC.
Try to answer this question if possible: Which system was used in Soviet Union after all calculations?
Answer: 3 kV DC
Question: The two volume biography of Whitehead by Victor Lowe is the most definitive presentation of the life of Whitehead. However, many details of Whitehead's life remain obscure because he left no Nachlass; his family carried out his instructions that all of his papers be destroyed after his death. Additionally, Whitehead was known for his "almost fanatical belief in the right to privacy", and for writing very few personal letters of the kind that would help to gain insight on his life. This led to Lowe himself remarking on the first page of Whitehead's biography, "No professional biographer in his right mind would touch him."
Try to answer this question if possible:  Why was every Nachlass left behind after Whitehead's death?
Answer: unanswerable
Question: Alaska (i/əˈlæskə/) is a U.S. state situated in the northwest extremity of the Americas. The Canadian administrative divisions of British Columbia and Yukon border the state to the east while Russia has a maritime border with the state to the west across the Bering Strait. To the north are the Chukchi and Beaufort Seas, the southern parts of the Arctic Ocean. To the south and southwest is the Pacific Ocean. Alaska is the largest state in the United States by area, the 3rd least populous and the least densely populated of the 50 United States. Approximately half of Alaska's residents (the total estimated at 738,432 by the Census Bureau in 2015) live within the Anchorage metropolitan area. Alaska's economy is dominated by the fishing, natural gas, and oil industries, resources which it has in abundance. Military bases and tourism are also a significant part of the economy.
Try to answer this question if possible: Which industries are least prevalent in Alaska's economy?
Answer:
unanswerable