the amount of a radioactive isotope decays in half every year. The amount of the isotope can be modeled by f(x) = 346(1/2)^x and f(1) = 173. What does the 1 represent?

A) The starting amount of the isotope
B) The amount of the isotope after one year
C) The rate the isotope decreases
D) The number of years that have passed