One week, Isabelle bought 2 bags of apples and 3 bags of oranges. The next week, she bought 1 bag of apples and 2 bags of oranges. If a represents the cost of each bag of apples and r represents the cost of each bag of oranges, which expression could Isabelle use to calculate the difference between the amounts she spent each week?

A) 3a - r
B) 3a - 5r
C) (2a - 3r) - (a - 2r)
D) (2a + 3r) - (a + 2r)