A radioactive isotope decays at the rate indicated by the exponential function A (t) =800 (1/2) ^ t/1500, where “t” is the time in years and A(t) is the amount of the isotope, in grams, remaining what is the initial mass of the isotope?
A. 200 grams
B. 900 grams
C. 800 grams
D. 400 grams