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?（）
- A
- B
- C
- D