Final answer:
The lung fluke found in a dog on necropsy is likely Fasciola hepatica, which is a trematode that can occasionally be found in the lungs, although they typically infect the liver.
Step-by-step explanation:
The fluke found in the lung of a dog is most likely Paragonimus westermani, which is known as the oriental lung fluke. This is not one of the options provided, therefore, it's necessary to choose the answer that is a lung-invading parasite from the available options. Although Dirofilaria immitis, also known as heartworms, are nematodes and not flukes, they are often associated with the lungs as they can cause blockages there while they primarily inhabit the heart and blood vessels. However, since the question specifically asks for a fluke found in the lungs and the size matches approximately with flukes, Fasciola hepatica seems to be the most appropriate answer given that it is a fluke and can be found in ectopic sites outside of the liver (though rarely in the lungs). Options b), c), and d) are parasites that do not typically reside in the lung, making them less likely answers. Thus, the most accurate answer to this question, based on the information provided, would be b) Fasciola hepatica.