If $F\left(x\right)={\int }_3^x \left(2+\frac{d}{\mathrm{d}t}\cos t\right)\mathrm{d}t$ then $F^{\mathrm{\prime }}\left(\frac{\pi }{6}\right)$ is equal to

• A

  1/2 

• B

  2

• C

  3/4

• D

  3/2