Which of the Following Items Is Unique to the N-Tier

Which of the following items is unique to the N-tier architecture method of designing software applications?

A) Application layers can be separated, allowing each layer to be upgraded independently from other layers.
B) It is compatible with various databases including Access, Oracle, and SQL.
C) Data security is tied into each layer and must be updated for all layers when any upgrade is performed.
D) Application layers can be written in C, ASP.NET, or Delphi without any performance loss.