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?（）

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)]