人教选修八:Unit+5+Meeting+your+ancestors+listening,speaking+and+reading(共47张PPT)
人教选修八:Unit+5+Meeting+your+ancestors+listening,speaking+and+reading(共47张PPT)第4页

All living things have ______ in their bodies. When they die, the carbon ________________ at a ____ rate. The method measures __________ of carbon in bones or plants using radioactivity and can ________ how old the remains are.

starts to disappear

fixed

the amount

work out

carbon