Which of the contexts below represents linear growth?
a. a smartphone data plan charges a $50/month and $1.59/gb of data used.
b. a car depreciates at a rate of 3.3% per year.
c. the amount of a certain medication in a person's bloodstream decreases by start fraction, 2, divided by, 3, end fraction 3 2 ​ every month.
d. an elevator descends at a rate of 26 feet per second.