单项选择题 Assuming the tag library in the exhibit is imported with the prefix forum， which custom tag invocation produces a translation error in a JSP page？（）
单项选择题 Whichthe securitymechanismusestheconceptofarealm？（）
单项选择题 Whichthe basicauthenticationtypeisoptionalforaJ2EE1.4compliantwebcontainer？（）
Which JSTL tag structure supports this scenario？（）