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: In the Romantic era, the modern piano, with a more powerful, sustained tone and a wider range took over from the more delicate-sounding fortepiano. In the orchestra, the existing Classical instruments and sections were retained (string section, woodwinds, brass and percussion), but these sections were typically expanded to make a fuller, bigger sound. For example, while a Baroque orchestra may have had two double bass players, a Romantic orchestra could have as many as ten. "As music grew more expressive, the standard orchestral palette just wasn't rich enough for many Romantic composers."  New woodwind instruments were added, such as the contrabassoon, bass clarinet and piccolo and new percussion instruments were added, including xylophones, drums, celestes (a bell-like keyboard instrument), large orchestral harps, bells, and triangles  and even wind machines for sound effects. Question: What is a celestes?
[EX A]: a bell-like keyboard instrument

[EX Q]: Passage: In 2004, a large share of natural gas reserves in Iran were untapped. The addition of new hydroelectric stations and the streamlining of conventional coal and oil-fired stations increased installed capacity to 33,000 megawatts. Of that amount, about 75% was based on natural gas, 18% on oil, and 7% on hydroelectric power. In 2004, Iran opened its first wind-powered and geothermal plants, and the first solar thermal plant is to come online in 2009. Iran is the third country in the world to have developed GTL technology. Question: How much of Iran's 33k megawatt installed capacity was based on oil? 
[EX A]: 18%

[EX Q]: Passage: In 2008, Bloomberg claimed child labour in copper and cobalt mines that supplied Chinese companies in Congo. The children are creuseurs, that is they dig the ore by hand, carry sacks of ores on their backs, and these are then purchased by these companies. Over 60 of Katanga's 75 processing plants are owned by Chinese companies and 90 percent of the region's minerals go to China. An African NGO report claimed 80,000 child labourers under the age of 15, or about 40% of all miners, were supplying ore to Chinese companies in this African region. Amnesty International alleged in 2016 that some cobalt sold by Congo Dongfang Mining was produced by child labor, and that it was being used in lithium-ion batteries powering electric cars and mobile devices worldwide. Question: What is the cobalt used for?
[EX A]:
lithium-ion batteries powering electric cars and mobile devices worldwide