阅读理解。 More than three billion people are at risk from indoor air pollution because of the heating or cooking fuels they use. Most live in Africa, India and China. They use wood, crop waste, animal waste or coal. These solid fuels may be the least costly fuels available. But they are also a major cause of health problems and death. The Aprovecho Research Center has been designing cooking stoves for the developing world. People having less money use wood or biomass for cooking; the richer people use oil and gas. It's estimated that wood is running out more quickly than oil and gas. The group has made stoves using mud, bricks, sheet metal, clay, ceramics and old oil drums. Most of the stoves look like large, deep cooking pots. They have an opening at the bottom for the fire and a place on the top to put a pot. In the late 1970s, Aprovecho produced a popular stove called the Lorena. The Lorena was good at reducing smoke and warming homes. But new tests years later found that it was not efficient. The Lorena used twice as much wood as an open fire, and it took much longer to heat food. Since then, they have experimented with countless other designs. Their goal is to make an inexpensive stove-let's say five dollars-that makes little smoke, and it's safe for health and reduces global warming and deforestation(采伐森林)． Aprovecho has now partnered with a stove manufacturer in China. The company is making Aprovecho's first mass produced stoves. They are said to use 40%-50% less wood than an open fire, and produce 50%-70% less smoke. A company called StoveTec is selling them through its website for less than ten dollars. Dean Still says that more than one hundred thousand have been sold so far. 1. The underlined word 'biomass ' in Paragraph 2 refers to ________. A. oil and gas B. wood C. coal D. crop waste or animal waste 2. The following sentence is taken from the passage, it should be placed at the end of ________. The World Health Organization estimates that over 1,500,000 people a year die from breathing smoke from solid fuels. A. Paragraph 1. B. Paragraph 2. C. Paragraph 3. D. Paragraph 4. 3. Stoves designed by the Aprovecho Research Center should    be ________. ①luxurious ②costly ③efficient ④lowcarbon ⑤cleaner A．①②④ B．③④⑤ C．②③⑤ D．①③④