单项选择题 If a and b are integers and a-b=6，then a+b CANNOT be（）

单项选择题 If the sum of five consecutive even integers is 70，what is the value of the greatest of the five integers．（）

单项选择题 If r and 8 are positive integers，each greater than 1，and if 11(s-1)=13(r-1)，what is the least possible value of r+s（）