Which of the following packets is used by network devices running SNMPv1 to proactively send...

SNMPv1 uses Trap messages to send unsolicited notifications about network events (e.g., failures, threshold breaches).

Response (A): Sent as a reply to SNMP queries, not proactively.

Get-Next Request (C) and Get-Request (D): These are polling requests, not proactive alarms.

Thus, the correct answer is B (Trap).