You have built a web application that you license to small businesses. The webapp uses a context parameter， called licenseExtension， which enables certain advanced features based on your client’s licensepackage. When a client pays for a specific service， you provide them with a license extension key that theyinsert into the  of the deployment descriptor. Not every client will have this contextparameter so you need to create a context listener to set up a default value in the licenseExtensionparameter. Which code snippet will accomplish this goal？（）

• A、
• B、
• C、
• D、