Giardia is an important waterborne disease. this organism is a select one:

a. virus

b. protozoan

c. bacterium

d. fungus

Giardia is a microscopic parasite that causes the diarrheal illness known as giardiasis. Giardia  is found on surfaces or in soil, food, or water that has been contaminated with feces from infected humans or animals.

Explanation:

answer: land bridge theory. land bridge theory held that shifting portions of dry land explained the finding of identical species on different continents. plate tectonic theory eventually eliminated the land bridge theory.