Given $F(x)={\displaystyle \underset{2}{\overset{3x^2}{}}}(t^2+1)dt,F^{\text{'}}(x)=$

a$)(9x^4+1)(6x)$

b$)(9x^4+1)$

c$)9x^6+3x^2-\frac{14}{3}$

d$)9x^6+3x^2$