The problem: Answer a question about this article:
Early Muslim armies stayed in encampments away from cities because Umar feared that they might get attracted to wealth and luxury. In the process, they might turn away from the worship of God and start accumulating wealth and establishing dynasties. When Uthman ibn al-Affan became very old, Marwan I, a relative of Muawiyah I, slipped into the vacuum, became his secretary, slowly assumed more control and relaxed some of these restrictions. Marwan I had previously been excluded from positions of responsibility. In 656, Muhammad ibn Abi Bakr, the son of Abu Bakr, the adopted son of Ali ibn Abi Talib, and the great grandfather of Ja'far al-Sadiq, showed some Egyptians the house of Uthman ibn al-Affan. Later the Egyptians ended up killing Uthman ibn al-Affan.
Who was the great grandson of Muhammad ibn Ali Bakr?
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The answer: Ja'far al-Sadiq

The problem: Answer a question about this article:
Anti-miscegenation laws were passed in most states during the 18th, 19th and early 20th centuries, but this did not prevent white slaveholders, their sons, or other powerful white men from taking slave women as concubines and having multiracial children with them. In California and the western US, there were greater numbers of Latino and Asian residents. These were prohibited from official relationships with whites. White legislators passed laws prohibiting marriage between European and Asian Americans until the 1950s.
Were there any laws against marriage between whites and Asians in the US?
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The answer: White legislators passed laws prohibiting marriage between European and Asian Americans until the 1950s.

The problem: Answer a question about this article:
On tracks that London Underground share with National Rail third-rail stock (the Bakerloo and District lines both have such sections), the centre rail is connected to the running rails, allowing both types of train to operate, at a compromise voltage of 660 V. Underground trains pass from one section to the other at speed; lineside electrical connections and resistances separate the two types of supply. These routes were originally solely electrified on the four-rail system by the LNWR before National Rail trains were rewired to their standard three-rail system to simplify rolling stock use.
How did it become possible to share the voltage for different types of train?
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The answer: the centre rail is connected to the running rails

The problem: Answer a question about this article:
The early settlement was often subject to attack from sea and land, including periodic assaults from Spain and France (both of whom contested England's claims to the region), and pirates. These were combined with raids by Native Americans, who tried to protect themselves from so-called European "settlers," who in turn wanted to expand the settlement. The heart of the city was fortified according to a 1704 plan by Governor Johnson. Except those fronting Cooper River, the walls were largely removed during the 1720s.
Which group raided the settlement as a means to protect themselves from settlers?
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The answer:
Native Americans