Question: What parameter identifies a previously negotiated transfer policy for background data transfer in the Nnef_ChargeableParty_Create request message sent by the ASP to the NEF?
Option 1: Sponsoring Status
Option 2: Background Data Transfer Reference ID
Option 3: Flow description information
Option 4: External Application Identifier
Explanation: The correct answer is Background Data Transfer Reference ID, as it identifies a previously negotiated transfer policy for background data transfer as defined in clause 4.16.7. This parameter is used to inform the NEF about the agreed-upon transfer policy for background data transfer, which is essential for proper handling of sponsored data traffic.