Answer: Selection bias
Explanation:
From the question, we are informed that a travel agency contacted a department store and obtained the list of all people who made purchases using their credit cards at the store in the last month. The agency then surveyed a random sample from the list, calling them to ask their preference for air travel or train travel for taking holidays.
The bus depicted above is referred to as the selection bias. The selection bias is simply a bias that is introduced when the sample obtained is not a representation of the population that the researcher wants to analyze. Here, the study population doesn't represent the target population.
The list gotten was for the people who made purchases using their credit cards but the agency used the list to determine the preference for air travel or train travel for taking holidays. This shows selection bias.