Answer to Question 1
ANS: A
Mortality rates are informative only for fatal diseases and do not provide direct information about the level of existing disease or the risk of getting a particular disease. Because the popula-tion changes during the course of a year, typically an estimate of the population at midyear is taken as the denominator for annual rates, because the midyear population approximates the amount of person-time contributed by the population during a given year.
Answer to Question 2
ANS: B
An agent includes infectious organisms, such as Salmonella, chemical agents, and physical agents. Genetic susceptibility is considered to be a characteristic of a host. Human population distribution and climate are considered to be characteristics of the environment.