One week, Isabella bought two bags of apples and three bags of oranges. The next week, she bought one bag of apples and two bags of oranges. If a represents the cost of each bag of apples and are represents the cost of each bag of oranges, which expression could Isabella used to calculate the difference between the amount she spent each week? A: 3a-r
B: 3a-r
C: (2a-3r)-(a-2r)
D: (2a+3r)-(a+2r)