Match the parameterizations (I)-(IV) with the surfaces (a)-(d). In all cases $0 \leq s \leq \pi / 2,0 \leq t \leq \pi / 2$. Note that only part of the surface may be described by the given parameterization.
(a) Cylinder
(b) Plane
(c) Sphere
(d) Cone
I. $x=\cos s, \quad y=\sin t, \quad z=\cos s+\sin t$
II. $x=\cos s, y=\sin s, \quad z=\cos t$
III. $x=\sin s \cos t, y=\sin s \sin t, \quad z=\cos s$
IV. $x=\cos s, \quad y=\sin t, \quad z=\sqrt{\cos ^2 s+\sin ^2 t}$