Protozoan and helminthic diseases are difficult to treat because a. Their cells are structurally and functionally similar to human cells. b. They replicate inside human cells. c. They don't have ribosomes. d. They don't reproduce. e. They have more genes than bacteria.

(a) is the correct option

Explanation:

Protozoan and helminthic diseases are structurally and functionally similar to human cells

Protozoans

Protozoans are microscopic, one-celled organisms that can either be free-living or parasitic in natureBecause of their property to multiply in humans,it contributes to their survival and also allows serious infection to develop from just a single organismTransmission of protozoa which lives in a human’s intestine to another human(normal) occurs through a fecal-oral route (for example, can occur through contaminated food or water or person-to-person contact)

Helminths

Helminths are large, multicellular organisms that are normally visible to the naked eye in their adult stagesJust like protozoa, helminths can either be free-living or parasitic in natureBut in their adult form, helminths cannot multiply in humansHelminths which are known to be human parasites include: Flatworms– includes tapewormsRoundworms or nematodes– adult forms of these type of worms can reside in the gastrointestinal tract, blood, lymphatic system or subcutaneous tissues