正如所说别人，你需要比正则表达式更跟踪的话：

As said by others, you need more than a regex to keep track of words:

var words = new HashSet<string>();
string text = "I like the environment. The environment is good.";
text = Regex.Replace(text, "\\w+", m =>
                     words.Add(m.Value.ToUpperInvariant())
                         ? m.Value
                         : String.Empty);