A Scatterplot of the Price of a Book (Y Variable)

Multiple Choice

A scatterplot of the price of a book (y variable) versus the number of pages in the book (x variable) is shown for 15 books in a professors office. In addition, the symbol "o" shows that the book was a hardcover book, while the symbol "+" shows that the book was a softcover book. What is the main difficulty with using a regression line to analyze these data?

A) Presence of one or more outliers
B) Inappropriately combining groups
C) Curvilinear data
D) Response variable is not quantitative