Which situation represents a proportional relationship?
A The cost of m months of a gym membership, where there is a $250 startup fee and a
per month fee.
B The cost of n t-shirts, where each t-shirt costs $19.99 plus an additional $1.75 each for tax.
C The cost of purchasing b books at a bookstore, where each paperback book is $12 and each hardbound book is $20
D The cost of riding r rides at the fair, where the admission to the fair is
$12.75 and each ride costs $1.50