Integrate the following expression: (3x² + 1)/(x³ + x² + x + 1)dx. Which of the following is the correct indefinite integral of the expression?
A. ∫(3x² + 1)/(x³ + x² + x + 1)dx
B. ∫(3x² + 1)/(x³ + x² + x + 1)
C. ∫(3x² + 1)/(x³ + x² + x + 1)dx
D. ∫(3x² + 1)/(x³ + x² + x + 1)