c# winforms how to disable the scrollbar of richtextbox

i have a customized scrollbar, however i have tried my best to m开发者_高级运维ake the original one from windows invisible by using the customized one covering on it, it can not be done.

any one have idea of how remove the original scrollbar ?

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this.richTextBox1.ScrollBars = System.Windows.Forms.RichTextBoxScrollBars.None;