One of the Two Cautions About Using the Standard Deviation

One of the two cautions about using the standard deviation approach with the AB design is that:

A) this approach should not be used if the treatment scores are progressing in a way that indicates that the client is improving at a steady pace once the treatment is started
B) this approach should not be used if the baseline scores are progressing in a way that indicates that the client is improving at a steady pace even before the treatment is started
C) when the treatment scores are moving in the hypothesized direction at a level that would seem noteworthy
D) when the treatment scores are moving in the hypothesized direction