问题
单项选择题
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．Ⅱand Ⅲ
答案
参考答案：C
解析：
由图表中图书的库存信息无法得到学校X与学校Y的学生的多少，所以Ⅰ肯定不对；Ⅱ中涉及库存图书的平均年龄，学校X库存图书的平均年龄为：8×15%+7×10%+6×19%+5×23%+4×13%+3×12%+2×8%=5.23，学校Y库存图书的平均书龄为：8×12%+7×8%+6×13%+5×20%+4×18%+3×21%+2×8%=3.91，所以Ⅱ一定正确，其实由图表也可观察到学校X的年龄比较大的图书所占的比例均大于学校Y的，从而可判断Ⅱ是正确的；由两学校的库存总量不同，可推知Ⅲ肯定不对。