public boolean deleteBipolarQuesion(BipolarQuestion bipolarQuestion) {
		Element bipolarQuestionE;
		boolean flag = false;
		for (Iterator i = root.elementIterator("bipolarQuestion"); i.hasNext();) {
			bipolarQuestionE = (Element)i.next();
			if (bipolarQuestionE.element("id").getText().equals(bipolarQuestion.getId())) {
				bipolarQuestionE.element("isDelete").setText("true");
				System.out.println("has delete bipolar");
				// Write to xml
				try {
					XmlUtils.write2Xml(fileName, document);
					return true;
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				flag = true;
				break;
			} 
		}
		return flag;
	}