Tính 

Câu hỏi: Tính $I=\int 3x^5\sqrt{x^3+1}dx$

A. $I=\frac{1}{5}{\left(x^3+1\right)}^2\sqrt{x^3+1}-\frac{1}{3}\left(x^3+1\right)\sqrt{x^3+1}+C$

B. $I=\frac{2}{5}{\left(x^3+1\right)}^2\sqrt{x^3+1}-\frac{2}{3}\left(x^3+1\right)\sqrt{x^3+1}+C$

C. $I=\frac{2}{5}{\left(x^3+1\right)}^2\sqrt{x^3+1}+C$

D. $I=\frac{2}{5}{\left(x^3+1\right)}^2\sqrt{x^3+1}+\left(x^3+1\right)\sqrt{x^3+1}+C$