Visual Basic.NET - Enlazar dos combobox

Private Sub FrmRemision_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load

    conexion = New OleDbConnection(ConexionDatos.conectar())

    adaptadorCliente = New OleDbDataAdapter("SELECT cliente, id FROM CLIENTE WHERE activo = true", conexion)

    construct = New OleDbCommandBuilder(adaptador)

    datos = New DataSet()

    conexion.Open()

    adaptadorCliente.Fill(datos, "CLIENTE")

    conexion.Close()

    cboCliente.DataSource = datos.Tables("CLIENTE")

    cboCliente.DisplayMember = "cliente"

    cboCliente.ValueMember = "id"

    'cboCliente.SelectedIndex = -1

End Sub

Private Sub cboCliente_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboCliente.SelectedIndexChanged

    If cboCliente.SelectedIndex >= 0 Then

        Dim conexion As New OleDbConnection(ConexionDatos.conectar()) 'cadena conexion 

        Dim SelectedValue As String = "SELECT contrato, id FROM CONTRATO where idCliente=" + cboCliente.SelectedValue.ToString

        Dim comando As New OleDbCommand(SelectedValue, conexion)

        Dim adap As New OleDbDataAdapter(comando)

        datos = New DataSet()

        conexion.Open()

        adap.Fill(datos, "CONTRATO")

        conexion.Close()

        cboContrato.DataSource = datos.Tables("CONTRATO")

        cboContrato.DisplayMember = "contrato"

        cboContrato.ValueMember = "id"

    End If

End Sub