Mine

// Set up the basic controls
			contentPanel = new Gtk.Frame();

			vbox = new VBox();
			vbox.HeightRequest = 60;
			hbox = new HBox(true, 5);
			classCombo = new Gtk.ComboBox(); 
			membersCombo = new Gtk.ComboBox();
			
			// Setup the columns and column renders for the comboboxes
			
			CellRenderer colr = new CellRendererText();
			classCombo.PackStart(colr, true);
			classCombo.AddAttribute(colr, "text", 0);
			
			
			hbox.PackStart(membersCombo, false, true, 5);
			hbox.PackStart(classCombo, false, true, 5);
			vbox.PackEnd(hbox, false, false, 0);
			contentPanel.Add(vbox);