the solid lies between planes perpendicular to the x-axis at x=-1 and x=1. the cross-sections perpendicular to the x-axisare

a. circles whose diameters stretch from the curve $y=-\frac{1}{\sqrt{1+{x}^{2}}}$ to the curve $y=\frac{1}{\sqrt{1+{x}^{2}}}$

b. vertical squares whose base edges run along the same ends

a. circles whose diameters stretch from the curve $y=-\frac{1}{\sqrt{1+{x}^{2}}}$ to the curve $y=\frac{1}{\sqrt{1+{x}^{2}}}$

b. vertical squares whose base edges run along the same ends