An ancient bone contains 1/8 of the amount of carbon-14 found in living organisms. How old is the bone?

(a) 5,715 years (one C-14 half-life) 

(b) 11,430 years (two C-14 half-lives)

(c) 17,145 years (three C-14 half-lives) 

(d) 22,860 years (four C-14 half-lives)