c# – 来自StreamReader.ReadLine()的字符串的编码是什么

//The encoding of utf8.txt is UTF-8
StreamReader reader = new StreamReader(@"C:utf8.txt",Encoding.UTF8,true);
while (reader.Peek() > 0)
{
    //What is the encoding of lineFromTxtFile?
    string lineFromTxtFile = reader.ReadLine();
}

正如乔尔在着名的article中所说：

If you have a string,in memory,in a file,or in an email message,you have to know what encoding it is in or you cannot interpret it or display it to users correctly.”

所以这里有我的问题：字符串lineFromTxtFile的编码是什么？ UTF-8(因为它来自以UTF-8编码的文本文件)？或UTF-16(因为.NET中的字符串是“Unicode”(UTF-16))？

谢谢.