vb.net ComboBox1

 Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Me.MaximizeBox = False
        ComboBox1.DisplayMember = "管公稱直徑"
        ComboBox1.Items.Add("3/8B (10A)") '0
        ComboBox1.Items.Add("1/2B (15A)") '1
        ComboBox1.Items.Add("3/4B (20A)") '2
       。
       。
        ComboBox2.DisplayMember = "管公稱直徑"
        ComboBox2.Items.Add("焊管 Q235-A,Q235-B GB/T13793,T<=12") '0
        ComboBox2.Items.Add("焊管 20 GB/T13793,t<=12.7") '1
        ComboBox2.Items.Add("無縫管 10 GB9948,t<=16") '2
        ComboBox2.Items.Add("無縫管 10 GB6479 GB/T8163,t<=15") '3
       。
       。
End Sub

Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        If ComboBox1.SelectedIndex = 0 Then GoTo CMB15A
        If ComboBox1.SelectedIndex = 1 Then GoTo CMB15A
        If ComboBox1.SelectedIndex = 2 Then GoTo CMB20A
        If ComboBox1.SelectedIndex = 3 Then GoTo CMB25A
        If ComboBox1.SelectedIndex = 4 Then GoTo CMB40A
        If ComboBox1.SelectedIndex = 5 Then GoTo CMB40A
        If ComboBox1.SelectedIndex = 6 Then GoTo CMB50A
End Sub