My themes has been have a juqery link.
When I use Post Rating Plugin, My header will have a link /wp-includes/js/jquery/jquery.js?ver=1.7.1
So I have two jquery file in theme.
The plugins file (post-ratings/post-ratings.php) include
add_action('wp_enqueue_scripts', array($this, 'assets'));
when I remove this row, the plugins can't work.