您可能需要阅读 RichTextBox控件 [ ^ ]。在那里，你会发现以选择开头的各种属性。使用SelectionStart和SelectionLength属性，您可以在其中选择文本，然后使用其他属性更改所选文本，例如SelectionFont。

You might want to read the documentation on the RichTextBox control[^]. There, you'll find various properties beginning with "Selection". Use the SelectionStart and SelectionLength properties where you can select text and then use the other properties to make changes to the selected text, such as SelectionFont.