In a Memory Experiment,participants Are Asked to Learn a List

Multiple Choice

In a memory experiment,participants are asked to learn a list of words and then are tested on the list and the number of words they recall is recorded.In total,participants will be learning three word lists.Each of the word lists is of equivalent difficulty,the first list contains proper nouns,the second list contains breeds of dogs,and the third is a list of kitchen appliances.After working with 20 participants,the researchers notice that participants are better at recalling the proper nouns,the first list of the three that they learn.How can the researchers be certain that proper nouns are actually easier to recall and are not recalled better because they are the first words participants learn?

A) vary the dependent variable between conditions.
B) take a random sample of the participants' answers.
C) add a control group that only learns proper nouns.
D) counterbalance the order of the word lists.