正解:A
The application layer is the highest layer of the OSI model, and it provides the interface between the user and the network. It does not handle the details of packet delivery, such as addressing, routing, error checking, or encryption. Those functions are performed by the lower layers of the OSI model. The application layer only focuses on the format, content, and presentation of the data.
References:
Understanding the OSI Model - N10-008 CompTIA Network+ : 1.11
CompTIA Network+ Certification Exam Objectives, page 92