// A client program // In source file client.cs /* Namespace N1 public class C1 Namespace N2 internal class C2 public class C3 Namespace N3 public class C4 */ using N1; using N2; using N2.N3; public class Client{ C1 v = new C1(); // The type or namespace name 'C2' could not be found. // C2 w = new C2(); C3 x = new C3(); C4 y = new C4(); }