Tìm nguyên hàm
$\displaystyle \int{{\cos x{{{\sin }}^{2}}x}}dx.$
A. $\displaystyle \frac{1}{3}{{\cos }^{3}}x+C.$
B. $\displaystyle \frac{1}{3}{{\sin }^{3}}x+C.$
C. $\displaystyle -{{\sin }^{3}}x+2{{\cos }^{2}}x.\sin x+C.$
D. $\displaystyle \sin x({{\sin }^{2}}x+2{{\cos }^{2}}x)+C.$