我的联动怎么就没效果呢？

<!DOCUMENT>

<head>

<script>
    function lian() {
        var level = new Array("一线城市", "二线城市", "三线城市");
        var one = document.getElementById("s1");
        for (i = 0; i < 3; i++) {
            var opt = document.createElement("option");
            opt.value = i;
            opt.innerText = level[i];
            one.appendChild(opt);
        }

    }

    function changeValue() {
        var one = document.getElementById("s1");
        var two = document.getElementById("s2");
        var a = new Array("北京", "上海", "广州");
        var b = new Array("南京", "深圳", "长沙");
        var c = new Array("常德", "益阳", "衡阳");
        var sel = one.value;
        if (sel == 2) {
            for (i = 0; i < 3; i++) {
                var opt_1 = document.createElement("opiton");
                opt_1.value = i;
                opt_1.innerText = a[i];
                two.appendChild(opt_1);
            }
        }
    if (sel == 1) {
        for (i = 0; i < 3; i++) {
            var opt_1 = document.createElement("opiton");
            opt_1.value = i;
            opt_1.innerText = b[i];
            two.appendChild(opt_1);
        }
    }
    if (sel == 0) {
        for (i = 0; i < 3; i++) {
            var opt_1 = document.createElement("opiton");
            opt_1.value = i;
            opt_1.innerText = c[i];
            two.appendChild(opt_1);
        }
    }
    }
</script>

</head>
<html>

<select id="s1" onchange="changeValue()">
</select>

<select id="s2">
</select>

</body>

</html>

似乎木有看到change事件啊骚年

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