If you see a person carelessly throw a cigarette to the ground, what are you likely to think? If you hate people throwing things on the ground, you might think, "That person shouldn't litter." If you are a smoker, you might think, "I would sure like a cigarette right now." Most likely, though, you are not thinking, "That unused cigarette butt could be used to make something amazing!" That is, unless you are a creative scientist. If you are, you may see potential--a possibility--where others simply see trash . That is just what has happened in South Korea. The spirit of invention can hit at the strangest times and in the most unusual places. In South Korea, it happened near a trash can. Kin Gil-Pyo is with  the Seoul National University. He says he saw people  throwing away cigarette butts, which got him thinking. He began wondering if something useful could be made from them. He and other researchers found a way to convert cigarette butts into materials required for high-performance batteries. Kim Gil-Pyo says they looked closely at used cigarette filters , the parts of cigarettes smokers put into their mouths. Filters are made of a material called "cellulose acetate ." Mr. Kim explains that cellulose acetate can be made into another material: carbon. The pieces of cellulose acetate, known as fibers, are changed through a one-step burning process. After this, they are turned into an energy storage material. But why use carbon? Carbon has many qualities that seem  to make it the perfect material. Carbon has a high surface area. It conducts electricity well. It also stays stable, unlikely to change, for a long time. And carbon does not cost a lot. All these qualities make it the most popular material for making super-capacitors . Super-capacitors are good at storing energy. They have high-power mass, or density . They require only a short time for recharging. And they have a long lifecycle. Super-capacitors are used in products such as laptop computers and cell phones. They are also used in industrial energy converters, like wind turbine machines. Combining carbon and super-capacitors seems like a perfect marriage. Kim Gil-Pyo tells the Reuters News Agency that cigarette butts could affect the economy is a huge way. They could prove to be a low-cost source of carbon material. They are so cheap that smokers throw them to the ground. And you don't get much cheaper than that. The story tells the readers the truth that  _  .
where there is a will, there is a way the most useless is usually the most useful ideas usually hit at the most unusual places one person's trash is another person's treasure
Question: If you see a person carelessly throw a cigarette to the ground, what are you likely to think? If you hate people throwing things on the ground, you might think, "That person shouldn't litter." If you are a smoker, you might think, "I would sure like a cigarette right now." Most likely, though, you are not thinking, "That unused cigarette butt could be used to make something amazing!" That is, unless you are a creative scientist. If you are, you may see potential--a possibility--where others simply see trash . That is just what has happened in South Korea. The spirit of invention can hit at the strangest times and in the most unusual places. In South Korea, it happened near a trash can. Kin Gil-Pyo is with  the Seoul National University. He says he saw people  throwing away cigarette butts, which got him thinking. He began wondering if something useful could be made from them. He and other researchers found a way to convert cigarette butts into materials required for high-performance batteries. Kim Gil-Pyo says they looked closely at used cigarette filters , the parts of cigarettes smokers put into their mouths. Filters are made of a material called "cellulose acetate ." Mr. Kim explains that cellulose acetate can be made into another material: carbon. The pieces of cellulose acetate, known as fibers, are changed through a one-step burning process. After this, they are turned into an energy storage material. But why use carbon? Carbon has many qualities that seem  to make it the perfect material. Carbon has a high surface area. It conducts electricity well. It also stays stable, unlikely to change, for a long time. And carbon does not cost a lot. All these qualities make it the most popular material for making super-capacitors . Super-capacitors are good at storing energy. They have high-power mass, or density . They require only a short time for recharging. And they have a long lifecycle. Super-capacitors are used in products such as laptop computers and cell phones. They are also used in industrial energy converters, like wind turbine machines. Combining carbon and super-capacitors seems like a perfect marriage. Kim Gil-Pyo tells the Reuters News Agency that cigarette butts could affect the economy is a huge way. They could prove to be a low-cost source of carbon material. They are so cheap that smokers throw them to the ground. And you don't get much cheaper than that. The story tells the readers the truth that  _  .
A. where there is a will, there is a way
B. the most useless is usually the most useful
C. ideas usually hit at the most unusual places
D. one person's trash is another person's treasure
Answer: