This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

[EX Q]: Passage: 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. Question: What nowdays electrification systems can use?
[EX A]: DC motors which directly use the DC or they may be 3-phase AC motors

[EX Q]: Passage: In Eastern Europe, Byzantium revived its fortunes under Emperor Basil I (r. 867886) and his successors Leo VI (r. 886912) and Constantine VII (r. 913959), members of the Macedonian dynasty. Commerce revived and the emperors oversaw the extension of a uniform administration to all the provinces. The military was reorganised, which allowed the emperors John I (r. 969976) and Basil II (r. 9761025) to expand the frontiers of the empire on all fronts. The imperial court was the centre of a revival of classical learning, a process known as the Macedonian Renaissance. Writers such as John Geometres (fl. early 10th century) composed new hymns, poems, and other works. Missionary efforts by both eastern and western clergy resulted in the conversion of the Moravians, Bulgars, Bohemians, Poles, Magyars, and Slavic inhabitants of the Kievan Rus'. These conversions contributed to the founding of political states in the lands of those peoplesthe states of Moravia, Bulgaria, Bohemia, Poland, Hungary, and the Kievan Rus'. Bulgaria, which was founded around 680, at its height reached from Budapest to the Black Sea and from the Dnieper River in modern Ukraine to the Adriatic Sea. By 1018, the last Bulgarian nobles had surrendered to the Byzantine Empire. Question: During what century did John Geometres flourish?
[EX A]: 10th

[EX Q]: Passage: At the age of 10, West moved with his mother to Nanjing, China, where she was teaching at Nanjing University as part of an exchange program. According to his mother, West was the only foreigner in his class, but settled in well and quickly picked up the language, although he has since forgotten most of it. When asked about his grades in high school, West replied, "I got A's and B's. And I'm not even frontin'." Question: What University was the cause of West's mother moving the family to China?
[EX A]:
Nanjing University