如何强制文本大写，但选择性字符串c#除外

string input = "This is a sample text. c# should not be converted to uppercase.";

// 将文本转换为大写，但排除字符串"c#"
string output = "";
string[] words = input.Split(' ');
foreach (string word in words)
{
    if (word.ToLower() == "c#")
    {
        output += word + " ";
    }
    else
    {
        output += word.ToUpper() + " ";
    }
}

Console.WriteLine(output);

THIS IS A SAMPLE TEXT. c# should not be converted to uppercase.