If the average （arithmetic mean ) of x, y, z, 5 and 7 is 8, which of the following must be

If the average (arithmetic mean ) of x, y, z, 5 and 7 is 8, which of the following must be true？

I. The median of the five numbers cannot be 5.

II. At least one of x, y, and z is greater than 9.

III. The range of the five numbers is 2 or more

A．I only

B．II only

C．III only

D．I and III

E．II and III