什么是结构化分析方法？结构化分析的常用工具有哪些？
白居易前、后期思想变化对他的诗歌创作有何影响？试举例说明。
生物的大环境包括（）、（）和（）。
导叶封水不严密有何危害？
You are developing a Windows Communication Foundation (WCF) service. The service needs to access out-of-process resources.You need to ensure that the service accesses these resources on behalf of the originating caller. What should you do?（） [" Set the value of ServiceSecurityContext.Current.WindowsIdentity.ImpersonationLevel to TokenlmpersonationLevel.Impersonation"," Set the value of ServiceSecurityContext.Current.Windowsldentity.ImpersonationLevel to TokenlmpersonationLevel.Delegation"," Set the PrincipalPermissionAttribute on the service contract and update the binding attribute in the endpoint element of the configuration file to wsHttpBinding"," Set the PnncipalPermissionAttribute on the service contract and update the bindingConfiguration attribute in the endpoint element of the configuration file to wsHttpBinding"]
有害组分？
