The answer is D: allusion
The poetic technique illustrated throughout the entire poem "Happiness Epidemic" is allusion , which is the figure of speech the authors use to make a brief reference to a place, person, idea or event in order to make association from these sources. It is a reference to something or someone outside the text. The author mentions health/medical issues: Epidemic, disease, syntoms, clinically, major organs, virus etc to describe happiness and its effects.