【单选题】

If the average(arithmetic mean)of x，y，x，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