Explanation:

The scenario involves:
Integrating a phone system with the Service Console.
This type of integration is done through Salesforce Open CTI (Computer Telephony Integration).
To connect the phone system and Salesforce, you must install and configure a CTI adapter provided by the telephony vendor or built custom with Open CTI.

Why B is correct
The CTI adapter is the essential link between the phone system and Salesforce.
Once configured, it enables features like:
Screen pops with caller information
Click-to-dial from Salesforce
Call logging directly into records
Without configuring the adapter, the integration will not function.

📖 Reference:
Salesforce Help – Integrate Your Telephony System with Salesforce — Configuring the CTI adapter is a required step for phone integration.

Why the others are incorrect
A. Enable the Lightning Console
The console is already in use in the Service Cloud environment.
While necessary for the interface, enabling the console alone doesn’t integrate the phone system.
C. Add the utility bar to the app
The utility bar can hold the softphone widget (after CTI setup), but just adding it doesn’t establish the integration.
It’s a supporting step after the CTI adapter is configured.

💡 Summary:
The CTI adapter is the core technical piece for Service Console telephony integration — without it, enabling console features or utility bars won’t connect the phone system.