What does pop function do in the following code?

for$($int $i=0$;$i<mn\; id="EditorElement\_3854162">1</mn>$;$i++)$

$\{$

a$.$ pop$(ch)$;

if $($ch $!=$s$[$i$])$

$\{$

flag$=1$;

break;

$\}$

$\}$

A$.$ remove one item from stack and save it in a$.$

B$.$ peek one item from stack and save it in char.

C$.$ remove one item from stack and save it in char.

D$.$ sends char to stack called a$.$