Concept: Use substitution to reduce the integrand to a partial fraction form.Explanation: Multiply numerator and denominator by x2 so that the derivative of x3 appears.Let I=∫x(x3+1)dx=∫x3(x3+1)x2dx.Put x3=t, then 3x2dx=dt.So I=31∫t(t+1)dt.Using partial fractions: t(t+1)1=t1−t+11.Thus I=31∫(t1−t+11)dt=31(ln∣t∣−ln∣t+1∣)+c.Simplify: I=31lnt+1t+c.Substitute t=x3: I=31lnx3+1x3+c.This equals ln(3x3+1x3)+c.Answer: Option C: log(3x3+1x3)+c, where c is the constant of integration.