C# WebBrowser控件读html流并显示

//环境VS2005，WinXPSP2
//test.txt 为html源代码
private void Form1_Load(object sender, EventArgs e)
{
string str = null;
StreamReader sr = new StreamReader("D:\test.txt", Encoding.Default);
webBrowser1.Navigate("about:blank");
webBrowser1.Document.OpenNew(true);
str = sr.ReadToEnd();
webBrowser1.Document.Write(str);
}