For Some Research Designs, One of the Weaknesses of the Single-Subject

For some research designs, one of the weaknesses of the single-subject research study is ______.

A) the treatment effect (i.e., the possibility that the treatment is ineffective even though the data revealed an improvement in client scores)
B) the carryover effect (i.e., the possibility that the effect of the treatment will carry over from the treatment period to a subsequent baseline period)
C) the subsequent syndrome (i.e., the fact that clients might show improvement during the treatment period)
D) the handover syndrome (i.e., the handing over of the scores to a researcher will compromise the ethics of the study)