Mac ID binds to specific phone but baSE setting binds to all physical phone. I think this is what question was asking

As confusing as the question is, this one is D. The website states, "ou then identify a specific phone using the appropriate options, such as a MAC address for a hardware [physical] phone or a remote address for a remote phone." https://help.mypurecloud.com/articles/phone-configuration-overview/

Phone settings The phone settings allow you to identify a specific phone and then configure how that phone is to operate in Genesys Cloud by assigning it a corresponding base settings configuration. When you create a phone, you begin by assigning the phone an appropriate name and then you select the base settings configuration. You then identify a specific phone using the appropriate options, such as a MAC address for a hardware phone or a remote address for a remote phone. In addition, you’ll need to select a site. At this point, you can save the phone and it automatically inherits the default configuration specified in the base settings. Alternatively, you can customize the phone by altering any of the settings that it inherited from the base settings configuration-without affecting the original base settings configuration.

MAC address as far "physical phone".

Question says you are creating phone config (phone in CX) to associate with a physical phone. And to link this phone config with physical phone you need to set MAC in config. So answer D. B answer only links phone template with phone config, but still you do not have any linkage to physical phone there. In Basic settings you do not set linkage to physical phone.

I think MAC Address as the mention "to a physical phone".

Terrible question, I still don't konw the answer after reading https://help.mypurecloud.com/articles/phone-configuration-overview/

B https://help.mypurecloud.com/articles/phone-configuration-overview/