Context and question: Railways must operate at variable speeds. Until the mid 1980s this was only practical with the brush-type DC motor, although such DC can be supplied from an AC catenary via on-board electric power conversion. Since such conversion was not well developed in the late 19th century and early 20th century, most early electrified railways used DC and many still do, particularly rapid transit (subways) and trams. Speed was controlled by connecting the traction motors in various series-parallel combinations, by varying the traction motors' fields, and by inserting and removing starting resistances to limit motor current.
All early electrified motors used what type of motor?
Answer: unanswerable
Context and question: Imamah (Arabic: ) is the Shia Islam doctrine (belief) of religious, spiritual and political leadership of the Ummah. The Shia believe that the Imams are the true Caliphs or rightful successors of Muhammad, and further that Imams are possessed of divine knowledge and authority (Ismah) as well as being part of the Ahl al-Bayt, the family of Muhammad. These Imams have the role of providing commentary and interpretation of the Quran as well as guidance to their tariqa followers as is the case of the living Imams of the Nizari Ismaili tariqah.
What is the Shia Islam doctrine called?
Answer: Imamah
Context and question: In January 2010, Hong Kong-based English newspaper The Standard reported that writer Tan Zuoren attempted to document shoddy construction that may have led to massive casualties in schools, was sentenced to in prison ostensibly for his writing an article in 2007 in support of the pro-democracy movement in 1989.
When did the sentencing occur?
Answer:
in 2007