Answer: B.population
Explanation:
We know that a lurking variable is a variable that is not included in the analysis as an explanatory variable or response variable but it can affect the results of the analysis of relationships between variables.
In statistics, the population represents a very large group of participants that have at least one common feature.
Given: In a study of towns there was a positive correlation between the number of mail boxes and number of traffic lights in a town. But it actually depends on the population too. So the interpretation here can be affected by the population.
Therefore, the population is most likely the lurking variable that explains the correlation .