Question: The London Underground in England is one of the few networks that uses a four-rail system. The additional rail carries the electrical return that, on third rail and overhead networks, is provided by the running rails. On the London Underground, a top-contact third rail is beside the track, energized at +420v DC, and a top-contact fourth rail is located centrally between the running rails at −210v DC, which combine to provide a traction voltage of 630v DC. London Underground is now upgrading its fourth rail system to 750v DC with a positive conductor rail energised to +500v DC and a negative conductor rail energised to -250v DC. However, many older sections in tunnels are still energised to 630v DC. The same system was used for Milan's earliest underground line, Milan Metro's line 1, whose more recent lines use an overhead catenary or a third rail.
Is there an answer to this question: What type of system does London Underground use?

Answer: four-rail system


Question: Because the duchy was outside of the core Holy Roman Empire, the prince-electors of Brandenburg were able to proclaim themselves King of Prussia beginning in 1701. After the annexation of most of western Royal Prussia in the First Partition of the Polish-Lithuanian Commonwealth in 1772, eastern (ducal) Prussia was connected by land with the rest of the Prussian state and was reorganized as a province the following year (1773). Between 1829 and 1878, the Province of East Prussia was joined with West Prussia to form the Province of Prussia.
Is there an answer to this question: What type of government entity was Prussia prior to 1773?

Answer: unanswerable


Question: The modern Standard Chinese exonym for the ethnic Tibetan region is Zangqu (Chinese: 藏区; pinyin: Zàngqū), which derives by metonymy from the Tsang region around Shigatse plus the addition of a Chinese suffix, 区 qū, which means "area, district, region, ward". Tibetan people, language, and culture, regardless of where they are from, are referred to as Zang (Chinese: 藏; pinyin: Zàng) although the geographical term Xīzàng is often limited to the Tibet Autonomous Region. The term Xīzàng was coined during the Qing dynasty in the reign of the Jiaqing Emperor (1796–1820) through the addition of a prefix meaning "west" (西 xī) to Zang.
Is there an answer to this question: How do the Chinese refer to Tibetan people, language, and culture?

Answer: Zang


Question: Horizontal gene transfer refers to the transfer of genetic material through a mechanism other than reproduction. This mechanism is a common source of new genes in prokaryotes, sometimes thought to contribute more to genetic variation than gene duplication. It is a common means of spreading antibiotic resistance, virulence, and adaptive metabolic functions. Although horizontal gene transfer is rare in eukaryotes, likely examples have been identified of protist and alga genomes containing genes of bacterial origin.
Is there an answer to this question: What is one trait that horizontal gene transfer is a common means of spreading?

Answer:
antibiotic resistance