VB.NET
* Public Class Form1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
WebBrowser1.Navigate("http://aa")
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim elements As HtmlElementCollection = WebBrowser1.Document.All

For Each webpageelement As HtmlElement In elements

If webpageelement.GetAttribute("id") = "aaa" Then
webpageelement.InvokeMember("click")
End If
Next
End Sub
End Class