<?php if ($t['current_engine_id'] == 1) : ?>
        Ad code for engine ID 1
    <?php elseif ($t['current_engine_id'] == 1) : ?>
        Ad code for engine ID 1
    <?php endif; ?>
    <div class="ad-unit">
        <?php echo get_option('ad_unit_3'); ?>
    </div>
</div>
<?php endif; ?>