Apopulation of bacteria is treated with an antibiotic. it is estimated that 5,000 live bacteria existed in the sample before treatment. after each day of treatment, 40% of the sample remains alive. which best describes the graph of the function that represents the number of live bacteria after x days of treatment?

a. f(x) = 5000(0.4)x, with a horizontal asymptote of y = 0

b. f(x) = 5000(0.6)x, with a vertical asymptote of x = 0

c. f(x) = 5000(1.4)x, with a horizontal asymptote of y = 0

d. f(x) = 5000(1.6)x, with a vertical asymptote of x = 0