A clinical trial investigated the effectiveness of a new cognitive behavioral therapy app for reducing symptoms of insomnia in young adults. Forty-two participants aged $20$ to $22$ with chronic insomnia were randomly assigned to use either the cognitive behavioral therapy app or a relaxation music app for six weeks. Sleep quality was assessed at the start and end of the study. What are the experimental units and the treatments in this experiment?

• A. Experimental units: $42$ young adults with insomniaTreatments: cognitive behavioral therapy app and relaxation music app for six weeks
• B. Experimental units: cognitive behavioral therapy and relaxation music appsTreatments: $42$ young adults with insomnia
• C. Experimental units: sleep quality scoresTreatments: cognitive behavioral therapy app and relaxation music app for six weeks
• D. Experimental units: $42$ young adults with insomniaTreatments: sleep quality assessment

Answer: (A)