A solid is constructed between the lines x=a\displaystyle {x}={a}, x=b\displaystyle {x}={b}, the graph of y=f(x)\displaystyle {y}={f{{\left({x}\right)}}} and the x-axis so that the cross-sections of the solid are circles perpendicular to the x-axis, as shown in the figure.

Which of the following integrals represents the volume of this solid?