Refer to the exhibit. An engineer must invoke a Python script that alerts the operations team when the router DC-RTR-1 becomes unreachable. Which configuration set accomplishes this task?

`track 3 ip sla 10 reachability` defines a tracking object for an IP SLA operation but does not, by itself, invoke a script or configure an event-driven automation for unreachability.

`scheduler job name ROUTER-DOWN` is used to configure scheduled tasks that run at specific times or intervals, not for event-driven automation based on a network state change like unreachability.

`event scheduler name DOWN-ROUTER` is a command typically related to scheduling events, similar to `scheduler job`, and is not used for real-time, event-triggered automation of scripts in response to network state changes.

The `event manager applet` command initiates the configuration of a Cisco EEM applet, which is designed to automate responses to network events. By configuring an EEM applet to monitor an IP SLA track object for reachability, it can detect when DC-RTR-1 becomes unreachable and then execute a configured action, such as running a Python script to alert the operations team.