Answer:
The correct answer is the spread of disease among the passengers.
Explanation:
A biologist who studies the spread of disease among the passengers traveling in a flight would be an epidemiologist. An epidemiologist refers to a scientist who examine studies within the populations of individuals. These are the public health professionals who assess the outbreaks of the disease in order to cure the prevailing diseases and to inhibit the outbreaks in future. They are regarded as the disease detectives of the public health world.