Which of the choices below is one of the primary gases found in the atmosphere? a. oxygen b. carbon dioxide c. argon d. helium

Oxygen is your answer. :)

Epidemiology. Epidemiology is the science that studies the epidemics - it studies quantitatively the distribution of the health and sickness phenomena and its conditioning factors in human populations. Epidemiology is very important when it comes to the identifying of risk factors for disease and where to act in order to develop a preventive health care.