We are looking for a function whose derivative is x³. From the power rule for derivatives, it ought to be a function involving a higher power of x. This gives us two choices: B or D.

To check choice B, take the derivative of x⁴/4 + C. You get 4x³/4, and the 4's cancel to leave x³. So, choice B is the correct choice. Choice D uses the "dx" wrongly; it belongs with the integral sign -- see the definition box above.