Well first off I would say you need to show us what code you have that isn't doing what you expect. I have no idea where in the output that echo should be showing up based on what you said to say why it doesn't do what you expect.
Secondly when building the <option>s you have to check if the current option is the one previously selected by the user, if it is you need to use the selected="selected" html attribute. Below you will find a basic function I use to build simple <select>s I hope it illustrates and helps.
function buildSelect(Array $options,$name,$selected) {
$str = '<select name="'.$name.'">'."\n";
foreach( $options as $k => $v ) {
$str .= '<option value="'.$k.'"'.($selected==$k?' selected="selected"':'').'>'.$v.'</option>'."\n";
}
$str .= '</select>'."\n";
return $str;
}