Which of the following statements correctly determines the rule for generating the next term in the sequence 23, 19.5, 16, 12.5, . . .?

The common difference between the terms is decreasing by 3.5 each time. Thus, the rule for generating the next term in the sequence is to subtract 3.5 from the previous term. Therefore the next term is $12.5 - 3.5 = \boxed{9}$.