Claudio is conducting a study on mindfulness meditation. One group in his study is instructed to practice meditating for 30 minutes per day and the other group is asked to take a 30-minute walk each day while listening to their favorite music. He decides to give a mindfulness inventory questionnaire to his participants to check if the meditation group actually demonstrated mindfulness. This practice is known as .a) variable check
b) manipulation check
c) validity check
d) debriefing