Your Web site processes book orders. One of the application methods contains the following code segment. XmlDocument doc = newXmlDocument（　）; doc.LoadXml(“10”+” ”); You need to remove the discount element from XmlDocument. Which two code segments can you use to achieve this goal? (Each correct answer presents a complete solution. （）

• A、XmlNode root = doc.DocumentElement;root.RemoveChild(root.FirstChild);
• B、XmlNode root = dec.DocumentElement;root.RemoveChild(root.SelectSingleNode(“discount”));
• C、doc.RemoveChild(doc.FirstChild);
• D、doc.DocumentElement.RemoveChild(doc.FirstChild);