x$2+$ y$2=9$

Here

x$2+$ y$2=9$

with no restrictions on $?$x$$y$$z $,$ so a point in the region must lie on a circle of radius and center on the $?$x$$y$$z $-$axis, but it could be in any horizontal plane

$?$x$$y$$z $=$ k

$($parallel to the $?$xy$$yz$$xz $-$plane$).$ Thus, the region consists of all possible circles

x$2+$ y$2=9,$

$?$x$$y$$z $=$ k

and is therefore a $---$Select$---$circle$$sphere$$circular cylinder with radius whose axis is the $?$x$$y$$z $-$axis.