If a cat has an infection and the doctor is unsure where the infection is the doctor chooses the drug based on?

This is apparently a question in an exam somewhere, and there are posts claiming B (based on location of action), C (based on widest effect) and D (based on primary effect).

In the real world, a veterinarian would generally not prescribe anything at all without knowing at least the organ or tissue that had the infection - this is a basic piece of information that drives the antibiotic choice. For example, an infection in the ear may be treated with topical eardrops, but a veterinarian would never prescribe antibiotic ear drops for a bladder infection. Some infections are in hard to access places, such as in the brain or in the joint - these infections may require special antibiotics or injections directly into the affected location.