DrLonsbary Is a Cognitive Psychologist Who Is Curious About How

Dr.Lonsbary is a cognitive psychologist who is curious about how mood affects memory.She recruited 60 high school students and divided them into three groups.Group A listened to a five-minute piece of music intended to make them feel happy (a song titled "Don't Worry,Be Happy") .Group B listened to a five-minute piece of music intended to make them feel sad (a song titled "Alone Again") .Group C listened to no music and instead was asked to sit quietly for five minutes (thought to make them feel neutral) .
When a participant would come to her laboratory,Dr.Lonsbary would greet the participant and then ask him or her to draw a card.Participants who drew a 1,2,or 3 were assigned to Group A.Participants who drew a 4,5,or 6,were assigned to Group B.Participants who drew a 7,8,or 9,were assigned to Group C.The participants were then given an unlabeled CD to listen to based on their group assignment.The CD contained either the song selection or five minutes of silence.They were then escorted into a different room,where they were greeted by a research assistant who conducted the experiment.The research assistant sat the participants in front of a computer screen and told them that a list of 25 words would be displayed on the screen.They were instructed to listen to the CD with headphones while trying to memorize the list of words.All participants were given the same list of 25 words to remember.
When five minutes had passed,the screen displayed a question asking them whether they felt happy,sad,or neutral.After the participant responded,a new screen was displayed asking them to type in all the words they could remember from the list of 25 words.All participants were given three minutes to type the words they remembered.Afterward,the participant was thanked and dismissed.In response to the mood question,a majority of Group A participants said they were happy,a majority of Group B participants said they were sad,and a majority of Group C participants said they were neutral in their mood.Dr.Lonsbary found the following results in response to the number of words remembered.
-Dr.Lonsbary's decision to randomly assign participants to the three groups was done to avoid which of the following?

A) An order effect
B) A selection effect
C) A practice effect
D) A carryover effect