[单选题]
The ideal battery will store a lot of energy in a small package．Right now, Belcher's model battery, a metallic disk completely built by viruses, looks like a regular watch battery. But inside, its components are very small—so tiny you can only see them with a powerful microscope．Which of the following is true of Belcher's battery mentioned in paragraph 6?
A .It is made of metal．
B .It is a kind of watch battery．
C .It can only be seen with a microscope．
D .It is a metallic disk with viruses inside it．
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