怎么弹不出对话框？
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>score</title>
<script type="text/javascript">
function rec(){
var score;
score=prompt("请输入你的成绩");
if(score>=90){
document.write("你很棒");
}
else if(score>=75){
document.write("还不错");
}
else if(score>=60){
document.write("及格了");
}
else{
document.write("不及格");
}
</script>
</head>
<body>
<input name="button" type="button" onClick="rec()" value="点击我，弹出对话框" />
</body>
</html>
如图，少个大括号
