Problem: Railway electrification system:

Modern electrification systems take AC energy from a power grid which is delivered to a locomotive and converted to a DC voltage to be used by traction motors. These motors may either be DC motors which directly use the DC or they may be 3-phase AC motors which require further conversion of the DC to 3-phase AC (using power electronics). Thus both systems are faced with the same task: converting and transporting high-voltage AC from the power grid to low-voltage DC in the locomotive. Where should this conversion take place and at what voltage and current (AC or DC) should the power flow to the locomotive? And how does all this relate to energy-efficiency? Both the transmission and conversion of electric energy involve losses: ohmic losses in wires and power electronics, magnetic field losses in transformers and smoothing reactors (inductors). Power conversion for a DC system takes place mainly in a railway substation where large, heavy, and more efficient hardware can be used as compared to an AC system where conversion takes place aboard the locomotive where space is limited and losses are significantly higher. Also, the energy used to blow air to cool transformers, power electronics (including rectifiers), and other conversion hardware must be accounted for.

Modern electrification systems take DC energy from what?
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A: unanswerable

Problem: On January 9, 1957, Karachay Autonomous Oblast and Chechen-Ingush Autonomous Soviet Socialist Republic were restored by Khrushchev and they were transferred from the Georgian SSR back to the Russian SFSR.
What republic had the Karachay Autonomous Oblast previously been a part of?
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Answer: the Georgian SSR

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Haredi Judaism advocates segregation from non-Jewish culture, although not from non-Jewish society entirely. It is characterised by its focus on community-wide Torah study. Haredi Orthodoxy's differences with Modern Orthodoxy usually lie in interpretation of the nature of traditional halakhic concepts and in acceptable application of these concepts. Thus, engaging in the commercial world is a legitimate means to achieving a livelihood, but individuals should participate in modern society as little as possible. The same outlook is applied with regard to obtaining degrees necessary to enter one's intended profession: where tolerated in the Haredi society, attending secular institutions of higher education is viewed as a necessary but inferior activity. Academic interest is instead to be directed toward the religious education found in the yeshiva. Both boys and girls attend school and may proceed to higher Torah study, starting anywhere between the ages of 13 and 18. A significant proportion of students, especially boys, remain in yeshiva until marriage (which is often arranged through facilitated dating see shiduch), and many study in a kollel (Torah study institute for married men) for many years after marriage. Most Orthodox men (including many Modern Orthodox), even those not in Kollel, will study Torah daily.
What is not a legitimate means of livelihood in Haredi society?
A: unanswerable

Context and question: The officials in Mexico City reduced the price of corn from six cents to two cents a pound. The northern portion of the state continued to decline economically which led to another revolt led by G. Casavantes in August 1879; Governor Trias was accused of misappropriation of funds and inefficient administration of the state. Casavantes took the state capital and occupied it briefly; he was also successful in forcing Governor Trias to exile. Shortly afterwards, the federal government sent an entourage led by Trevino; Casavantes was immediately ordered to resign his position. Casavantes declared political victory as he was able to publicly accuse and depose Governor Trias. At the same time the states of Durango and Coahuila had a military confrontation over territorial claims and water rights; this altercation between the state required additional federal troops to stabilize the area. Later a dispute ensued again among the states of Coahuila, Durango, and Chihuahua over the mountain range area known as Sierra Mojada, when large deposits of gold ore was discovered. The state of Chihuahua officially submitted a declaration of protest in May 1880 that shortly after was amicably settled. Despite the difficulties at the beginning, Diaz was able to secure and stabilize the state, which earned the confidence and support of the people.
Durango and Coahuila had a military confrontation over what natural resource?
Answer: water

Question: Due to the 1973 spike in oil prices, the economy of Iran was flooded with foreign currency, which caused inflation. By 1974, the economy of Iran was experiencing double digit inflation, and despite many large projects to modernize the country, corruption was rampant and caused large amounts of waste. By 1975 and 1976, an economic recession led to increased unemployment, especially among millions of youth who had migrated to the cities of Iran looking for construction jobs during the boom years of the early 1970s. By the late 1970s, many of these people opposed the Shah's regime and began to organize and join the protests against it.
Is there an answer to this question: What caused inflation to Iran's economy during the oil price spike in 1973?

Answer: economy of Iran was flooded with foreign currency

Problem: Database:

The relational model also allowed the content of the database to evolve without constant rewriting of links and pointers. The relational part comes from entities referencing other entities in what is known as one-to-many relationship, like a traditional hierarchical model, and many-to-many relationship, like a navigational (network) model. Thus, a relational model can express both hierarchical and navigational models, as well as its native tabular model, allowing for pure or combined modeling in terms of these three models, as the application requires.

What is the relationship that is avoided in a navigational model?
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A:
unanswerable