单项选择题 One of the use cases in your web application uses many session-scoped attributes. At the end of the usecase， you want to clear out this set of attributes from the session object. Assume that this static variableholds this set of attribute names： 201.private static final Set<String> USE_CASE_ATTRS；  202.static { 203.USE_CASE_ATTRS.add（"customerOID"）； 204.USE_CASE_ATTRS.add（"custMgrBean"）； 205.USE_CASE_ATTRS.add（"orderOID"）； 206.USE_CASE_ATTRS.add（"orderMgrBean"）； 207.} Which code snippet deletes these attributes from the session object？（）

单项选择题 Whichstatementistrueaboutwebcontainersessionmanagement？（）

单项选择题 Your web application requires the adding and deleting of many session attributes during a complex usecase. A bug report has come in that indicates that an important session attribute is being deleted too soonand a NullPointerException is being thrown several interactions after the fact. You have decided to create asession event listener that will log when attributes are being deleted so you can track down when theattribute is erroneously being deleted. Which listener class will accomplish this debugging goal？（）