Final answer:
Adrian should include girls in the experiment to avoid experimental bias and ensure that the results are representative of all students. Other measures such as random assignment and a blind study design can further prevent bias.
Step-by-step explanation:
To avoid experimental bias, Adrian should include girls in the experiment since limiting the test subjects to only boys can skew the results and would not determine if the effect of listening to music while playing video games is universal. Including both boys and girls can help ensure that the sample is representative of all students and not just a subset. Furthermore, Adrian could take other steps to prevent bias such as randomly assigning the participants into different groups where one listens to music and the other does not, ensuring the video games and music are the same for all participants, and perhaps even use a blind study design where the scorer does not know who was listening to music.