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: Due to the expansion of trade and its geographical proximity, Kiev became the most important trade centre and chief among the communes; therefore the leader of Kiev gained political "control" over the surrounding areas. This princedom emerged from a coalition of traditional patriarchic family communes banded together in an effort to increase the applicable workforce and expand the productivity of the land. This union developed the first major cities in the Rus' and was the first notable form of self-government. As these communes became larger, the emphasis was taken off the family holdings and placed on the territory that surrounded. This shift in ideology became known as the verv'. Question: How did the leader of Kiev gain political control?
[EX A]: Due to the expansion of trade

[EX Q]: Passage: As war broke out, Maglione, Tardini and Montini were the main figures in the Vatican's State Department, as despatches originated from or addressed to them during the war years.[page needed] Montini was in charge of taking care of the "ordinary affairs" of the Secretariat of State, which took much of the mornings of every working day. In the afternoon he moved to the third floor into the Office of the Private Secretary of the Pontiff. Pius XII did not have a personal secretary. As did several popes before him, he delegated the secretarial functions to the State Secretariat. During the war years, thousands of letters from all parts of the world arrived at the desk of the pope, most of them asking for understanding, prayer and help. Montini was tasked to formulate the replies in the name of Pius XII, expressing his empathy, and understanding and providing help, where possible. Question: What role did Montini fill for Pius XII?
[EX A]:
Private Secretary