a) If $\displaystyle F(x) = \int_{6}^{x} \dfrac{1}{t} \, dt$, then $F'(x) =$

b) If $\displaystyle F(x) = \int_{x}^{15} \dfrac{1}{t} \, dt$, then $F'(x) =$

c) If $\displaystyle F(x) = \int_{5}^{x^{6}} \dfrac{1}{t} \, dt$, then $F'(x) =$

c) If $\displaystyle F(x) = \int_{2 + \cos x}^{x^2 + 1} \dfrac{1}{t} \, dt$, then $F'(x) =$