## Calculus 8th Edition

plot $I$
When $u$ is set as constant, the $z$ component becomes constant. Hence, the grid curves must be parallel to $xy$ plane. When $v$ is set as constant, the $y$ component becomes constant. Hence, the grid curves must be parallel to $xz$ plane. Only plot $I$ has pair of grid curves such that one of them is parallel to $xy$ plane and the other is parallel to $xz$ plane.