Question: What are the basic building blocks used to describe layer 3 procedures in the mobile radio interface?
Option 1: Structured Procedures
Option 2: Protocol Control Entities
Option 3: Elementary Procedures
Option 4: Layer 3 Transactions
Explanation: The correct answer is "Elementary Procedures" because, according to the text, elementary procedures provided by the protocol control entities of the three sublayers (radio resource management, mobility management, and connection management) are used as basic building blocks to describe layer 3 procedures.