Assignment task: Trina is testing the effectiveness of an exercise program on the reduction of self-injurious behavior (SIB) for three clients at a day program. Trina collects data on the SIB of the three clients for several sessions and then implements the exercise program with the first client only. The exercise program is not implemented with the other two clients although data is still being collected on SIB for all three clients. After stable levels of data are obtained with the first client during the intervention phase, Tina continues running the exercise program with the first client and begins implementing it with the second client while still collecting data on SIB for all three clients. Finally, after stable data for the second client in the intervention phase is obtained, Tina continues running the exercise program with the first two clients and begins implementing it with the third client while collecting data on SIB for all three clients. Which experimental design is Trina using? Reversal Multielement Multiple baseline Changing criterion