Answers:

A. year, grade and interaction between year and grade

B. year, year-squared, grade and interaction year and grade

C. year

D. year and grade

E. year and year-squared

F. year, year-squared, and grade

Monitoring the Future is an ongoing study of the behaviors, attitudes, and values of American secondary school students, college students, and young adults. We will be looking at several regression models for predicting marijuana use each year for students enrolled in 8th, 10th and 12th grades, with tens of thousands of students across the United States participating in the survey each year. The graph below is for predicting y = Marijuana= % of students who report having used marijuana at least once from: x1 = Year (year of the survey, from 1991 to 2018) and x2 = Grade (entered as 8, 10, 12) Scatterplot of marijuana vs year 40 12 10 25 marijuana 20 15 " . 8 1990 1995 2000 2005 2010 2015 2020 year Which of predictor variables would be necessary to include in the model to get: three non-parallel curves [Choose ] three parallel curves [ Choose ] one curve [ Choose ] three non- parallel lines [ Choose ] three parallel lines [ Choose ] one line [Choose ]