Question: What is the primary purpose of the `extendedMAC-LengthField-r13` field in E-UTRA User Equipment (UE) radio access capabilities?
Option 1: To indicate UE support for a 16-bit length of the MAC Logical Channel Identifier (LCID) field.
Option 2: To specify the maximum number of HARQ processes supported by the UE.
Option 3: To define the minimum required Receive Sensitivity for the UE.
Option 4: To signal the UE's capability for enhanced Inter-Cell Interference Coordination (eICIC).
Explanation: The `extendedMAC-LengthField-r13` field is specifically related to the MAC layer, focusing on the length of a particular field. In this context, it pertains to extending the length of the MAC L (Logical Channel Identifier or potentially another relevant field) to 16 bits, enhancing flexibility or capacity in MAC layer communications as specified in the broader context of E-UTRA's MAC protocol specification. This directly aligns with Option 1, which correctly identifies the primary purpose of this field.