Find or evaluate the integral by completing the square. (Use C for the constant of integration.) ∫(x + x⁴ + 2x² + 2) dx
a) x² + x⁵ + 2x³ + 2x + C
b) (x + 1)² + (x² + 1)² + C
c) (x² + 1)² + (x⁴ + x²) + C
d) (x² + 1)² + (x³ + x) + C