Calculus 8th Edition

$IV$
Given that $r(u,v)=ucosvi+usinvj+vk$ To find the grid curves corresponding to $u$ as constant , substitute $u=k$ $r(k,v)=kcosvi+ksinvj+vk$ This is an equation of helix with circular orbits and constant radius $=k$ Only plot $IV$ and $V$ contain grid curves which are helix. But only plot $IV$ contains helical grid curves with constant radius.