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?（）
- A Apply the following attribute to the server assembly. [assembly: AllowPartiallyTrustedCallers(PartialTrustVisibilityLevel=VisibleToAllHosts)]
- B Apply the following attribute to the server assembly. [assembly: AllowPartiallyTrustedCallers(PartialTrustVisibilityLevel=NotVisibleByDefault)]
- C Apply the following attribute to the client assembly. [assembly: AllowPartiallyTrustedCallers(PartialTrustVisibilityLevel=VisibleToAllHosts)]
- D Apply the following attribute to the client assembly. [assembly: AllowPartiallyTrustedCallers(PartialTrustVisibilityLevel=NotVisibleByDefault)]