如何在RichTextBox控件中给文本加下划线?

大家好.现在，我正在制作一个用于测量打字速度的程序.我在表单上放置了一个RichTextBox控件，一个TextBox控件和一个按钮控件.当用户按下按钮时，速度测试开始.在这里，用户必须在文本框中输入相同的字符，并加载到RichTextBox控件中.我需要的是，一开始，RichTextBox的第一个字符下面必须有下划线，以便用户可以看到它，然后他在文本"框中输入该字符.然后，RichTextBox的第二个字符下方应有下划线，以便用户在文本框中输入相同的字符，依此类推.这个怎么做?请帮帮我.

Hi to all. Right now, I am making a Program which measures Typing speed. I have placed one RichTextBox control, one TextBox Control and one button control on the form.when user presses the button, speed Test starts.Here, User has to enter same characters in the text box, which are loaded in RichTextBox control. what I need is, at beginning, There must be underline below first character of RichTextBox, so that user can see it, and then he enters that character in Text box. Then there should be underline below second character of RichTextBox, so user enters same character in text box and so on. how to do this? please, help me.