Question: Which of the following messages is sent by the User Equipment (UE) to reject activation of a default Evolved Packet System (EPS) bearer context?
Option 1: DEACTIVATE EPS BEARER CONTEXT ACCEPT
Option 2: MODIFY EPS BEARER CONTEXT REQUEST
Option 3: ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT
Option 4: ESTABLISHMENT CAUSE REQUEST
Explanation: The correct answer is Option 3 because the ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT message is specifically defined as the message sent by the UE to reject activation of a default EPS bearer context, as per the provided text. This message type is used for this specific purpose in the Non-Access Stratum (NAS) protocol for Evolved Packet System (EPS).