The school’s guidance department compares the grade-point averages and standardized state test scores for 10 students in each grade. The table below shows the correlation coefficient for each data set.

Ok, so to see which data sets is reasonable for a linear regression model square each set and if it is close to one it will be reasonable. 

[tex]r^{2}[/tex]
9th grade 0.3 = [tex]0.3^{2}[/tex] = 0.09
10th grade –0.1 = [tex]-0.1^{2}[/tex] = 0.01
11th grade 0.2 = [tex]0.2^{2}[/tex] = 0.04
12th grade –0.8 = [tex]-0.8^{2}[/tex] = 0.64

So 12th grade data set is reasonable but the others are not because they are not remotely close to 1.