Graduation rate is one measure used to compare colleges in national publications. One such publication compared semester tuition against graduation rate, defined as the percentage of students who graduate within four years. A graph titled College comparisons has semester tuition (thousands of dollars) on the x-axis, and 4-year graduation rate (percentage) on the y-axis. Points are grouped together in a line with positive slope.
Which statement best explains the relationship between the variables?

Higher tuition causes students to graduate at higher rates.
Tuition does not appear to have an association with graduation rate.
More selective colleges tend to have higher tuition but lower graduation rates.
More selective colleges tend to have higher tuition and higher graduation rates.