0.44 Points Question 18 A study published in 2007 by Christopher Johnson, professor of music education and music therapy at the University of Kansas, revealed that students in elementary schools who took private music lessons scored around 20 percent higher in math scores on standardized tests, compared to students who did not take private music lessons. What is the explanatory variable? A Math score on standardized test B Grade level C Music therapy D Whether a student took private music lessons Question 19 0.43 Points