Protozoan diseases are usually spread through spore inhalation physical contact contaminated food or water cuts or other injury to the skin

c) Contaminated food

Explanation:

Protozoans are single-celled organisms that could be either free-living or parasitic. Free-living forms could inhabit in the soil, moss, and even in aquatic environments. On the other hand, parasitic protozoans need a host to develop and reproduce.

A protozoan gastrointestinal infection could be caused by the ingestion of cysts through contaminated food. For instance, giardiasis could be spread through the ingestion of contaminated food or water or directly from person to person. Amoebiasis is also an example of a gastrointestinal infection caused by the protozoan Entamoeba histolytica, which occurs through the ingestion of  food that is contaminated with animals' feces, this occurs especially in developing countries.

d. planting trees

the trees take in carbon to make oxygen.