Passage:…The nineteenth century brought with it a burst of new discoveries and inventions that revolutionized the candle industry and made lighting available to all. In the early-to-mid-nineteenth century, a process was developed to refine tallow (fat from animals) with alkali and sulfuric acid. The result was a product called stearin. Stearin is harder and burns longer than unrefined tallow. This breakthrough meant that it was possible to make tallow candles that would not produce the usual smoke and rancid odor. Stearins were also derived from palm oils, so vegetable waxes as well as animal fats could be used to make candles… Which of the following can be inferred from paragraph 1 about candles before the nineteenth century? a)They did not smoke when they were burned. b)They produced a pleasant odor as they burned. c)They were not available to all. d)They contained sulfuric acid. [解析]