final Label l1= toolkit.createLabel(composite,
				"C1");

final CCombo c1= new CCombo(composite,
				SWT.DROP_DOWN | SWT.BORDER);
		c1.setItems(new String[] { "A", "B" });
		final GridData gridData = new GridData(SWT.FILL, SWT.CENTER,
				true, false, 1, 1);
		c1.setLayoutData(gridData);

		final Label l2= toolkit.createLabel(composite,
				"C2");
				final CCombo c2 = new CCombo(composite, SWT.DROP_DOWN
				| SWT.BORDER);
		final GridData gd = new GridData(SWT.FILL, SWT.CENTER, true, false, 1,
				1);
		c2.setLayoutData(gd);

		Label l3= toolkit.createLabel(composite,
				"C3");
		CCombo c3 = new CCombo(composite, SWT.DROP_DOWN
				| SWT.BORDER);
		final GridData objgd = new GridData(SWT.FILL, SWT.CENTER,
				true, false, 1, 1);
		c3.setLayoutData(objgd);

c1.addSelectionListener(new SelectionAdapter() {
			public void widgetSelected(SelectionEvent e) {
				selectedText = c1.getText();
				if (selectedText.equalsIgnoreCase("A")) {
					gd.exclude = true;
				l2.setVisible(false);
					c2.setVisible(false);
					composite.layout(true);