\(\LARGE \int x^3 dx = \frac{x^4}{4}+C\)
So the answer is choice D. You can check this by differentiating the right hand side and you'll get x^3 back again.
This answer can be found by using the power rule for integrals. That rule is
\(\LARGE \int x^n dx = \frac{x^{n+1}}{n+1} + C\)
