A technician has just replaced a server that has been damaged by a lightning strike. A power protection device is installed on the new server. This is an example of:

Establishing a theory of probable cause occurs earlier in the troubleshooting process when the technician is hypothesizing what caused the original failure, not after the solution is being implemented.

Implementing preventive measures means taking action to prevent a known problem from occurring again after it has been identified. Installing a power protection device (such as a UPS or surge protector) directly addresses the vulnerability exposed by the lightning strike, protecting the replacement server from the same failure. This is a reactive-turned-preventive step in the troubleshooting methodology.

Root cause analysis is the process of determining the underlying reason a failure occurred - in this case, confirming the lightning strike caused the damage - not the act of installing protective hardware.

Escalating as appropriate refers to passing the problem to a higher-level technician or specialist when it is beyond the current technician's scope, which does not apply here.