Suppose a rectangular button within a UI is positioned so that its upper$-$left corner is at a location described as $100,320.$ The value $320$

a$.$ indicates that the upper$-$left corner of the button is $320$ units from the bottom of the screen

b$.$ indicates that the upper$-$left corner of the button is $320$ units from the left side of the screen

c$.$ is the $y-$coordinate

d$.$ is the $x-$coordinate