Which of the following algebraic expressions is not simplified?
A. 9x³y² +5x²y³ - 2x²y² + xy
3 2
2
B. -3a²b² +4ab² +6a²b-3ab
2.3
C. 2p²q² +2p²q²³ - 2p²q² + xy
D. 8m²n² +3m³n - 3n³m +9mn