Amy planted a flower garden with rows of blue flowers, b, and rows of yellow flowers, y. Each row of blue flowers has 5 flowers, and each row of yellow flowers has 7 flowers. Which expression represents the total number of flowers Amy planted?
A. 5 + r + 7 + b
B. 5b + 7y
C. 5 × 7 + b × y
D. 5y + 7b