Final answer:
Parasitic worms are studied in microbiology primarily because their diagnosis often requires the microscopic examination of samples to identify microscopic eggs and larvae. The correct option is D)
Step-by-step explanation:
Parasitic worms, even meters-long tapeworms, are studied in microbiology because diagnosis usually involves microscopic examination of patient samples. Although helminths, such as tapeworms and guinea worms, are multicellular and can be seen without a microscope, they are classified within microbiology mainly due to their microscopic eggs and larvae which are used for identification. Conditions like guinea-worm disease highlight the importance of understanding parasitic helminths in the realm of public health.