A park is studying how its population of deer grows over time. The regression line of their data is y = 15x+ 1200, where x represents the number of years since the study began and y represents the number of deer.
What does the slope of the regression line represent?
A The deer population will reach 1, 200 in 15 years.
B The deer population grows by 1, 200 every 15 years.
C There were 15 deer in the park at the beginning of the study.
D. For every 1 year, the deer population increased by an average of 15.
E For every 1 year, the deer population increased by an average of 1,200