options的remove用法

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <title>无标题文档 </title>
    </head>
    <script>
        function ss(num){
            document.getElementById("sss").options[num] = null;
            document.getElementById("sss").selecteIndex = 0
        }
    </script>
    <body>
        <select id="sss">
            <option value="0">0</option>
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
        </select>
        <input id="ff" type="text">
<input value="ss" type="button" onClick="ss(document.getElementById('ff').value)">
    </body>
</html>