Problem: Railway electrification system:

An early advantage of AC is that the power-wasting resistors used in DC locomotives for speed control were not needed in an AC locomotive: multiple taps on the transformer can supply a range of voltages. Separate low-voltage transformer windings supply lighting and the motors driving auxiliary machinery. More recently, the development of very high power semiconductors has caused the classic "universal" AC/DC motor to be largely replaced with the three-phase induction motor fed by a variable frequency drive, a special inverter that varies both frequency and voltage to control motor speed. These drives can run equally well on DC or AC of any frequency, and many modern electric locomotives are designed to handle different supply voltages and frequencies to simplify cross-border operation.

What was a disadvantage of DC system?
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A: power-wasting resistors


Problem: Hard rock:

Although Foo Fighters continued to be one of the most successful rock acts, with albums like In Your Honor (2005) reaching number two in the US and UK, many of the first wave of post-grunge bands began to fade in popularity. Acts like Creed, Staind, Puddle of Mudd and Nickelback took the genre into the 2000s with considerable commercial success, abandoning most of the angst and anger of the original movement for more conventional anthems, narratives and romantic songs. They were followed in this vein by new acts including Shinedown and Seether. Acts with more conventional hard rock sounds included Andrew W.K., Beautiful Creatures and Buckcherry, whose breakthrough album 15 (2006) went platinum and spawned the single "Sorry" (2007), which made the Top 10 of the Billboard 100. These were joined by bands with hard rock leanings that emerged in the mid-2000s from the garage rock or post punk revival, including Black Rebel Motorcycle Club and Kings of Leon, and Queens of the Stone Age from the US, Three Days Grace from Canada, Jet from Australia and The Datsuns from New Zealand. In 2009 Them Crooked Vultures, a supergroup that brought together Foo Fighters' Dave Grohl, Queens of the Stone Age's Josh Homme and Led Zeppelin bass player John Paul Jones attracted attention as a live act and released a self-titled debut album that reached the top 20 in the US and UK and the top ten in several other countries.

What year did Them Crooked Vultures release a self-titled debut album featuring Jet?
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A: unanswerable


Problem: Annelid:

Annelids' cuticles are made of collagen fibers, usually in layers that spiral in alternating directions so that the fibers cross each other. These are secreted by the one-cell deep epidermis (outermost skin layer). A few marine annelids that live in tubes lack cuticles, but their tubes have a similar structure, and mucus-secreting glands in the epidermis protect their skins. Under the epidermis is the dermis, which is made of connective tissue, in other words a combination of cells and non-cellular materials such as collagen. Below this are two layers of muscles, which develop from the lining of the coelom (body cavity): circular muscles make a segment longer and slimmer when they contract, while under them are longitudinal muscles, usually four distinct strips, whose contractions make the segment shorter and fatter. Some annelids also have oblique internal muscles that connect the underside of the body to each side.

What annelid is under the epidermis?
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A: unanswerable


Problem: Philadelphia:

Philadelphia's an annualized unemployment rate was 7.8% in 2014, down from 10.0%the previous year. This is higher than the national average of 6.2%. Similarly, the rate of new jobs added to the city's economy lagged behind the national job growth. In 2014, about 8,800 jobs were added to the city's economy. Sectors with the largest number of jobs added were in education and health services, leisure and hospitality, and professional and business services. Declines were seen in the city's manufacturing and government sectors.

What industries accounted for most of the city's job gains?
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A:
education and health services, leisure and hospitality, and professional and business services