如何在事先不知道类型的情况下反序列化XML?

[Serializable]
public class Base
{

    public string Property1 { get; set; }
    public int Property2 { get; set; }
}

[Serializable]
public class Sub: Base
{
    public List<string> Property3 { get; set; }

    public Sub():base()
    {
        Property3 = new List<string>();
    }        
}

Sub s = new Sub {Property1 = "subtest", Property2 = 1000};
s.Property3.Add("item 1");
s.Property3.Add("item 2");

XmlSerializer sFormater = new XmlSerializer(typeof(Sub));
using (FileStream fStream = new FileStream("SubData.xml", 
    FileMode.Create, FileAccess.Write, FileShare.None))
{
    sFormater.Serialize(fStream, s);
}

如何反序列化它们,以便返回正确的类?

XmlSerializer bFormater = new XmlSerializer(typeof (Base));
Base newBase;
using (FileStream fStream = new FileStream("BaseData.xml", 
    FileMode.Open, FileAccess.Read, FileShare.Read))
{
    newBase = (Base) bFormater.Deserialize(fStream);
}

除非我能够为从基派生的任何类传递一个XML文件,并创建正确的类。