单选题 下面的代码是实现了ServletRequestAttributeListener接口的类的部分代码,且该监听器已在DD中注册: public void attibuteAdded(ServletRequestAttributeEvent ev){ getServletContext(). log( "A: "+ ev. getName( )+ "->"+ ev.getValue()); } public void attibuteRemoved(ServletRequestAttributeEvent ev){ getServletContext().log("M:"+ ev_getName( ) + "->"+ ev.getValue()); } public void attibuteReplaced(ServletRequestAttributeEvent ev){ getServletContext().log( HP: M + ev. getName() + " ->" + ev.getValue ()); } 下面是一个Servlet中doGet()的代码: public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException,ServletException{ request.setAttibute("a", "b"); request.setAttibute("a", "c"); request.removeAttibute(na"); } 试问如果客户访问该Servlet,在日志文件中生成的内容为( )