d. One-shot case study
The reason why answer choice "d. One-shot case study" would be the correct answer because this would be a experimental design that has the least, or fewest, explanatory power compared to the other experimental designs.
A one-shot case stud is a study where students do not use any controlling factors and use only a single test group. Only one measurement would be taken after the study. The only thing that a one-shot case study would be measuring is the post-test results.
A "explanatory power" is pretty much a theory or hypothesis that one could make about a given subject and explain the subject very well and what causes it.
A one-shot case study doesn't have many factors that would help support a theory or hypothesis, due to the lack of evidence it would provide. This is why a one-shot case study would have the least explanatory power.
