Question: In E-UTRA, what does the `txAntennaSwitchDL-r13` field primarily indicate when present for a DownLink (DL) in a band combination?
Option 1: The total number of antennas used for transmission in the DL.
Option 2: The entry number of the first-listed UpLink (UL) band that affects this DL during transmit antenna switching.
Option 3: The frequency range within which the DL is operational when antenna switching occurs.
Option 4: Whether the UE supports Multiple Input Multiple Output (MIMO) in the specified DL.
Explanation: This field's purpose is to identify the specific UL band (by its entry number) that influences the behavior of the associated DL when transmit antenna switching happens, crucial for managing radio access capabilities efficiently in dynamic network conditions.