You upgrade a Windows Forms application to Microsoft .NET Framework 4. The application was developed
by using a previous version of the .NET Framework. The application uses the Code 
Access Security (CAS) policy for file access. 
When the application is executed, you receive the following exception:  
"NotSupportedException: This method uses CAS policy, which has been obsoleted by the .NET Framework." 
You need to resolve the error. 
What should you do?（）

You use Microsoft .NET Framework 4 to create an application.  
The application contains a partially trusted client assembly and a server assembly. 
You create a custom sandboxed application domain.  
You need to ensure that the application can be executed in a partial-trust environment. 
What should you do?（）