Which of the Following Is a Disadvantage of the One-Group

Which of the following is a disadvantage of the one-group pretest-posttest uninterpretable design?

A) The lack of information about any possible difference in the groups that exist before treatment makes it difficult to attribute results to the treatment.
B) The lack of a comparison group makes it impossible to rule out threats to internal validity.
C) The lack of random assignment of participants to groups allows the possibility that the groups may have differed along a number of important dimensions.
D) The lack of a control group makes it impossible to determine-after comparing pretest-posttest observations-if a change has occurred.