【正文】
hnique is only about 40 years old ARight B Wrong CNot mentioned 18 An atom of ordinary carbon has six protons and eight neutrons ARight B Wrong CNot mentioned 19 Radar is used to determine the characteristics of radiocarbon. ARight B Wrong CNot mentioned 20 Radiocarbon is reliable in dating an object back to at least 50,000 years. ARight B Wrong CNot mentioned 21 When an anism dies, the C14 in it begins to decay. ARight B Wrong CNot mentioned 22 The halflife of C14 is about 25,000 years. ARight B Wrong CNot mentioned