js用soap方式调用webservice ，参数传不进去

[zg_vera]

JS：
//在这处我们拼接
var data;
data = '<?xml version="1.0" encoding="utf-8"?>';
data = data + '<soap12:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap12="http://www.w3.org/2003/05/soap-envelope">';
data = data + '<soap12:Body>';
data = data + '<add xmlns="http://tempuri.org/" />';
data = data + '<num1>1</num1>';
data=data+'<num2>3</num2>';
data = data + '</soap12:Body>';
data = data + '</soap12:Envelope>';

//创建异步对象
var xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); //支持IE内核
xmlhttp.Open("POST", URL, false);
xmlhttp.SetRequestHeader("Content-Type", "application/soap+xml");
xmlhttp.Send(data);

document.getElementById("data3").innerHTML=xmlhttp.responseText;


webservice:

[WebMethod]
public int add(int num1,int num2)
{
int c = num1 + num2;
return c;
}

num1和num2的参数传不进去，这是为什么？？