Final answer:
Emphysema will result in the greatest attenuation of the beam.
Step-by-step explanation:
The pathologic condition that will result in the greatest attenuation of the beam is emphysema.
In emphysema, the walls of the alveoli in the lungs are destroyed, decreasing the surface area for gas exchange. This reduces the transmission of X-rays through the lungs, causing greater attenuation of the beam.
Therefore, the correct answer is A. Emphysema.