<?php
$options = array(
'value1' => 'content1',
'value2' => 'content2',
);
$active = isset($_POST['select']) ? $_POST['select'] : '';
?>
<select>
<?php foreach ($options as $value => $content) : ?>
<option<?=($value == $active) ? ' selected' : ''?> value="<?=$value?>"><?=$content?></option>
<?php endforeach ?>
</select>