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.

Example Input: 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?
Example Output: DC motors which directly use the DC or they may be 3-phase AC motors

Example Input: Passage: However questions still remain, as some of the corrupt government officials have still not been brought to justice, while the many families who lost their only child, are still seeking compensation and justice to what had happened. According to the Times, many parents were warned by the government not to stage a protest under the threat of arrest. Question: Who has not been brought to justice?
Example Output: corrupt government officials

Example Input: Passage: General Secretary and President Hu Jintao announced that the disaster response would be rapid. Just 90 minutes after the earthquake, Premier Wen Jiabao, who has an academic background in geomechanics, flew to the earthquake area to oversee the rescue work. Soon afterward, the Ministry of Health said that it had sent ten emergency medical teams to Wenchuan County. On the same day, the Chengdu Military Region Command dispatched 50,000 troops and armed police to help with disaster relief work in Wenchuan County. However, due to the rough terrain and close proximity of the quake's epicenter, the soldiers found it very difficult to get help to the rural regions of the province. Question: What was Premier Wen Jiabao's background in?
Example Output:
geomechanics