An example of a communicable disease is:
a. cancer
b. chronic respiratory disease
c. diabetes
d. giardiasis

The correct answer is option D, Giardiasis

Giardiasis is a communicable disease that is spread by the parasite Giardia. Giradiasis is a form of diarrhea and the causative parasite spread through water, soil and food which is contaminated with feces of infected humans and animals. This parasite is resistant to even chlorine disinfection as the outer shell protect it for a longer period of time.

b. the carbon cycle ensures living things have a source of hydrogen