A. InsideOne ei = eo.new InsideOne（）：
B. eo.InsideOne ei= co.new InsideOne（）：
C. InsideOne ei = EnclosingOne.new InsideOne（）：
D. EnclosingOne.insideOne ei = eo.new InsideOne（）：

A. it provides centralized request handling for incoming requests.
B. It forces resource authentication to be distributed across web components.
C. It reduces coupling between presentation-tier clients and underlying business services.
D. It can be added and removed unobtrusively， without requiring changes to existing  code.
E. It allows preprocessing and postprocessing on the incoming requests and outgoing  responses.