（一）A Nepali teenager has designed a 23 solar panel using human hair.Milan Karki, who is 18 years old and lives in a village in rural Nepal, used human hair to replace silicon, which is a common but ( 1) component of solar panels.By using hair as a ( 2) , Karki said that solar panels can be produced for around 23, a price tag that could be (3) if they were mass-produced.The solar panel works because melanin, the pigment (色素) that gives hair its color, is light (4) and can act a
