The half-life of a radioactive kind of element is 18 minutes. There are currently 32 grams of the element. Which function can be used to determine the amount remaining after x minutes?
A. f(x) = 18(.5)x/32
C. f(x) = 32(.5)x/18
B. f(x) = 32(18)x/2
D. f(x) = .5(32)x/18