A group of researchers want to investigate if a newly designed word puzzle game has a positive effect on improving the memory of adults living in the United States. They plan to have 100 randomly selected adults from the U.S. participate in the experiment. At the start of the experiment, every participant will take a memory test. Then, each participant will choose to be in either the control group or the treatment group. The adults in the treatment group will play the word puzzle game for 30 minutes per day for 2 weeks. The adults in the control group will not play the word puzzle game. After 2 weeks, everyone will take the memory test again. The researchers will compare everyone’s before and after scores. Identify the flaw in the design of this experiment.

A. The experiment does not have any children participating, so the researchers won’t be able to apply the results to the population of all people living in the U.S.
B. The experiment does not randomly place the participants in either the control group or treatment group since the participants are selecting which group they want to be in.
C. The experiment does not have enough participants for the researchers to acquire meaningful results.
D. The experiment does not last long enough for the researchers to acquire meaningful results.