Which of the following statements can be inferred from the graph？
I School X has a smaller enrollment than School Y.
II If the age of a book is the number of years since purchase, then the average (arithmetic mean) age of a book in the School Y inventory is less than that of a book in the School X inventory.
III According to the inventory, School X and School Y purchased the same number of textbooks in 1976.

A. None
B. I only
C. II only
D. I and II
E. II and III