Order the polynomial -x⁴y² + 7x³y³ - 3xy⁵ + 2x²y⁴ in descending powers of x.
a) 7x³y³ - x⁴y² + 2x²y⁴ - 3xy⁵
b) -x⁴y² + 7x³y³ - 3xy⁵ + 2x²y⁴
c) -x⁴y² + 7x³y³ + 2x²y⁴ - 3xy⁵
d) 7x³y³ + 2x²y⁴ - 3xy⁵ - x⁴y²