Web Forms :: Imagebutton Control - Button Became Dark Blue And Others Remain No Changes When Click Any One

I want to put five buttons: introduction, product, history, feedback, contact. And when I click any one button, that button became dark blue, and others remain, no changes. So I write the following code:

Protected Sub ImageButton1_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles ImageButton1.Click
ImageButton1.ImageUrl = "~/image/CHOICE INTRODUCTION BLUE.jpg"
ImageButton2.ImageUrl = "~/image/CHOICE PRODUCTS.jpg"
ImageButton3.ImageUrl = "~/image/CHOICE HISTORY.jpg"
ImageButton4.ImageUrl = "~/image/CHOICE FEEDBACK.jpg"
ImageButton5.ImageUrl = "~/image/CHOICE CONTACT.jpg"
End Sub
Protected Sub ImageButton2_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles ImageButton2.Click
ImageButton1.ImageUrl = "~/image/CHOICE INTRODUCTION.jpg"
ImageButton2.ImageUrl = "~/image/CHOICE PRODUCTS BLUE.jpg"
ImageButton3.ImageUrl = "~/image/CHOICE HISTORY.jpg"
ImageButton4.ImageUrl = "~/image/CHOICE FEEDBACK.jpg"
ImageButton5.ImageUrl = "~/image/CHOICE CONTACT.jpg"
End Sub
Protected Sub ImageButton3_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles ImageButton3.Click
ImageButton1.ImageUrl = "~/image/CHOICE INTRODUCTION.jpg"
ImageButton2.ImageUrl = "~/image/CHOICE PRODUCTS.jpg"
ImageButton3.ImageUrl = "~/image/CHOICE HISTORY BLUE.jpg"
ImageButton4.ImageUrl = "~/image/CHOICE FEEDBACK.jpg"
ImageButton5.ImageUrl = "~/image/CHOICE CONTACT.jpg"
End Sub
Protected Sub ImageButton4_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles ImageButton4.Click
ImageButton1.ImageUrl = "~/image/CHOICE INTRODUCTION.jpg"
ImageButton2.ImageUrl = "~/image/CHOICE PRODUCTS.jpg"
ImageButton3.ImageUrl = "~/image/CHOICE HISTORY.jpg"
ImageButton4.ImageUrl = "~/image/CHOICE FEEDBACK BLUE.jpg"
ImageButton5.ImageUrl = "~/image/CHOICE CONTACT.jpg"
End Sub
Protected Sub ImageButton5_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles ImageButton5.Click
ImageButton1.ImageUrl = "~/image/CHOICE INTRODUCTION.jpg"
ImageButton2.ImageUrl = "~/image/CHOICE PRODUCTS.jpg"
ImageButton3.ImageUrl = "~/image/CHOICE HISTORY.jpg"
ImageButton4.ImageUrl = "~/image/CHOICE FEEDBACK.jpg"
ImageButton5.ImageUrl = "~/image/CHOICE CONTACT BLUE.jpg"
End Sub

It is workable, however there is only one problem: when i debug it some times it is ok, but some few times the button suddenly became small.