After a corporate office upgraded its Ethernet wiring, a number of users are unable to...

The correct answer is B. Gather additional details.

According to the CompTIA troubleshooting process for the A+ certification exams1, the technician should gather additional details after testing a theory that is incorrect. This step helps to identify the problem more accurately and establish a new theory of probable cause. The other options are not appropriate for this stage of the troubleshooting process. Documenting the findings, escalating the problem, and identifying user changes are steps that should be done later in the process, after determining the cause and implementing a solution1.