RichTextBox on tabs at TabControl

Hi.

At press button creating new tabs at TabControl with RichTextBox on it:

string title = "Заметка " + (tabControl1.TabCount + 1).ToString();
TabPage myTabPage = new TabPage(title);
tabControl1.TabPages.Add(myTabPage);

var textBox = new RichTextBox();
myTabPage.Controls.Add(textBox);

I have a some problem, how can I use for example fontDialog for selected RichTxBx and others RichTexBox at others tabs, how can I clear a text of RichTextBox only at tab which a selected now?