test.cs

private void DsManager_PossibleMergeBlockTablesChanged(object sender, EventArgs e)
{
    // attach the available merge blocks to the combobox
    cbMergeBlocks.Text = "";
    cbMergeBlocks.DataSource =
        dsManager.PossibleMergeBlockTables.ToList<DataTableInfo>();
    cbMergeBlocks.DisplayMember = "TableName";
}

private void DsManager_PossibleMergeFieldColumnsChanged(object sender, EventArgs e)
{
    // attach the available merge fields to the combobox
    cbMergeFields.Text = "";
    cbMergeFields.DataSource =
        dsManager.PossibleMergeFieldColumns.ToList<DataColumnInfo>();
    cbMergeFields.DisplayMember = "ColumnName";
}