Picture the scene: the battery on your mobile phone has run out. You can't make any calls for help and no one can contact you. You are all alone - well, not quite. Just reach into your pocket and take out a piece of sugar.Put it into the battery, wait a minute, and you're back on the phone.                  Thanks to a couple of American scientists, this situation could become real.Swadesh Chaudhuri and Derek Lovely have invented the  "bacteria battery" - powered by bacteria that eats sugar and turns it into electricity.     "This is a special organism," Lovely said."You ean harvest enough electricity to power a cell phone battery for about four days from a spoonful of sugar."     In the past, bacteria batteries have been expensive and not long-lasting. But this battery uses more efficient bacteria that can turn 80 percent of sugar into electrical energy. This is 30 percent more than similar batteries can manage.    The bacteria battery could become as small as a household battery. It's also cheap and stable, as sugar can be taken from waste and crops.     But the sugar to electricity process is slow: it could take weeks for the bacteria to digest a cup of sugar.And it produces "greenhouse" gases which pollute the environment.     The scientists understand there is a lot more work to be done. "It is still young," said Lovely."Where we are now is where solar power was 20 0r 30 years ago."     But he believes the battery could be used in scientific equipment at the bottom of the ocean.Other ideas include using sugar in the blood to run medical devices in the human body, and taking sugar from animal waste to provide energy to power homes in rural areas. This passage is mainly about  _          .
how to change sugar into electricity a scientific invention of a new kind of bacteria battery a new way to reduce pollution caused by mobile phones a new kind of mobile phones and its future
Question: Picture the scene: the battery on your mobile phone has run out. You can't make any calls for help and no one can contact you. You are all alone - well, not quite. Just reach into your pocket and take out a piece of sugar.Put it into the battery, wait a minute, and you're back on the phone.                  Thanks to a couple of American scientists, this situation could become real.Swadesh Chaudhuri and Derek Lovely have invented the  "bacteria battery" - powered by bacteria that eats sugar and turns it into electricity.     "This is a special organism," Lovely said."You ean harvest enough electricity to power a cell phone battery for about four days from a spoonful of sugar."     In the past, bacteria batteries have been expensive and not long-lasting. But this battery uses more efficient bacteria that can turn 80 percent of sugar into electrical energy. This is 30 percent more than similar batteries can manage.    The bacteria battery could become as small as a household battery. It's also cheap and stable, as sugar can be taken from waste and crops.     But the sugar to electricity process is slow: it could take weeks for the bacteria to digest a cup of sugar.And it produces "greenhouse" gases which pollute the environment.     The scientists understand there is a lot more work to be done. "It is still young," said Lovely."Where we are now is where solar power was 20 0r 30 years ago."     But he believes the battery could be used in scientific equipment at the bottom of the ocean.Other ideas include using sugar in the blood to run medical devices in the human body, and taking sugar from animal waste to provide energy to power homes in rural areas. This passage is mainly about  _          .
A. how to change sugar into electricity
B. a scientific invention of a new kind of bacteria battery
C. a new way to reduce pollution caused by mobile phones
D. a new kind of mobile phones and its future
Answer: