Trudy subscribed to a television streaming service that charges $9 per month, with payment due in advance. The function c(m) represents the cost, in dollars, of m months of streaming.
What is the range of C(m)?
a. all whole numbers greater than or equal to 9
b. all real numbers less than or equal to 9
c. all integers less than or equal to 9
d. all multiples of 9 greater than or equal to 9