A Scatter Plot of Number of Teachers and Number of People

Multiple Choice

A scatter plot of number of teachers and number of people with college degrees for cities in Pennsylvania reveals a positive association. The most likely explanation for this positive association is:

A) Teachers encourage people to get college degrees, so an increase in the number of teachers is causing an increase in the number of people with college degrees.
B) Teaching is a common profession for people with college degrees, so an increase in the number of people with college degrees causes an increase in the number of teachers.
C) Cities with higher incomes tend to have more teachers and more people going to college, so income is a confounding variable, making causation between number of teachers and number of people with college degrees difficult to prove.
D) Larger cities tend to have both more teachers and more people with college degrees, so the association is explained by a third variable, the size of the city.