事件委托（万能委托）
....................\EventHandler
....................\............\EventHandler
....................\............\............\bin
....................\............\............\...\Debug
....................\............\............\EventHandler.csproj
....................\............\............\EventHandler.csproj.user
....................\............\............\obj
....................\............\............\...\Debug
....................\............\............\...\EventHandler.csproj.FileList.txt
....................\............\............\Program.cs
....................\............\............\Properties
....................\............\............\..........\AssemblyInfo.cs
....................\............\............\Student.cs
....................\............\EventHandler.sln