为什么只有一个函数显示出来了第二个没出来？
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>函数传参</title>
<script type="text/JavaScript">
function sum(x,y,z)
{
sum = x + y +z;
document.write(x+"、"+y+"、"+z+"和:"+sum+"<br/>");
}
sum(5,8,3);
sum(7,1,4);
</script>
</head>
<body>
</body>
</html>
