vb.net จะทำ combo box จังหวัด เขต แขวง จะต้องทำยังไงครับ

Public Class Form2

    Dim clsdb As New database

    Sub province1()
        Dim prosql As String = "select * from Province "
        Dim ds As DataSet

        ds = clsdb.querydataset(prosql)

        With ComboBox2
            .DisplayMember = "provincename"
            .ValueMember = "provinceid"
            .DataSource = ds.Tables(0)
            '.SelectionStart = 0
            .Text = "กรุณาเลือก"
        End With

    End Sub

    Sub province2()
        Dim prosql As String = "select * from Province "
        Dim ds As DataSet

        ds = clsdb.querydataset(prosql)

        With ComboBox5
            .DisplayMember = "provincename"
            .ValueMember = "provinceid"
            .DataSource = ds.Tables(0)
            '.SelectionStart = 0
            .Text = "กรุณาเลือก"
        End With
    End Sub

    Sub area1()
        ComboBox3.Text = ""
        Dim arsql1 As String = "select * from area,province where area.provinecid=province.provinceid and area.provinceid='" & ComboBox2.SelectedValue & "' "
        Dim ds1 As DataSet

        ds1 = clsdb.querydataset(arsql1)

        With ComboBox3
            .DisplayMember = "areaname"
            .ValueMember = "areaid"
            .DataSource = ds1.Tables(0)
            '.SelectionStart = 0
            .Text = "กรุณาเลือก"
        End With
    End Sub

    Sub area2()
        Dim arsql2 As String = "select * from area,province where area.provinecid=province.provinceid and area.provinceid='" & ComboBox5.SelectedValue & "' "
        Dim ds2 As DataSet

        ds2 = clsdb.querydataset(arsql2)

        With ComboBox6
            .DisplayMember = "areaname"
            .ValueMember = "areaid"
            .DataSource = ds2.Tables(0)
            '.SelectionStart = 0
            .Text = "กรุณาเลือก"
        End With
    End Sub

    Sub zone1()
        Dim zsql As String = "select * from zone,area where zone.areaid=area.areaid and zone.areaid='" & ComboBox3.SelectedValue & "' "
        Dim ds As DataSet

        ds = clsdb.querydataset(zsql)

        With ComboBox4
            .DisplayMember = "zonename"
            .ValueMember = "zoneid"
            .DataSource = ds.Tables(0)
            '.SelectionStart = 0
            .Text = "กรุณาเลือก"
        End With
    End Sub

    Sub zone2()
        Dim zsql As String = "select * from zone,area where zone.areaid=area.areaid and zone.areaid='" & ComboBox6.SelectedValue & "' "
        Dim ds As DataSet

        ds = clsdb.querydataset(zsql)

        With ComboBox7
            .DisplayMember = "zonename"
            .ValueMember = "zoneid"
            .DataSource = ds.Tables(0)
            '.SelectionStart = 0
            .Text = "กรุณาเลือก"
        End With
    End Sub



    '**************************************************************************************************************
    '**************************************************************************************************************
    '**************************************************************************************************************
    '**************************************************************************************************************

    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Label1.Text = DateAndTime.Now
        Button3.Visible = False
        Button4.Visible = False

        province1()
        province2()
    End Sub

    Private Sub ComboBox2_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox2.SelectedIndexChanged
        Dim arsql1 As String = "select * from area,province where area.provinceid='" & ComboBox2.SelectedValue & "' and area.provinecid=province.provinceid "
        Dim ds1 As DataSet

        ds1 = clsdb.querydataset(arsql1)

        With ComboBox3
            .DisplayMember = "areaname"
            .ValueMember = "areaid"
            .DataSource = ds1.Tables(0)
            '.SelectionStart = 0
            .Text = "กรุณาเลือก"
        End With
    End Sub
End Class