try like this
Dim cbo As String = Cboid.Text
Dim str As String = "SELECT DISTINCT(id) FROM sample where ID='" & cbo & "' order by id"
Dim ds1 As DataTable
ds1 = objbs.ExcuteQuary1(str)
CboGroup.DataSource = ds1
CboGroup.DisplayMember = "ID"
CboGroup.ValueMember = "ID"
CboGroup.SelectedIndex = -1
Public Function ExcuteQuary1(ByVal str As String) As DataTable
Try
Dim da As New SqlDataAdapter()
cmd.Connection = conopen()
cmd.CommandType = CommandType.Text
cmd.CommandText = str
da.SelectCommand = cmd
Dim dt As New DataTable()
da.Fill(dt)
Return dt
Catch ex As Exception
CloseConnection()
Return Nothing
Finally
CloseConnection()
End Try
End Function