Read the experimental design below and answer the question that follows. a researcher wants to determine the effects of sleep on memory and decides to schedule two groups of subjects for a sleep study. both groups will be asked to memorize as many items as they can from the same prepared list of items. then they will be allowed to go to sleep. in group a, the subjects will only be allowed to sleep for six hours. in group b, the subjects will be allowed to sleep for their usual amount of time. after each subject is finished sleeping, a quiz will be given over the list that was supposed to be memorized. what is the independent variable in the experiment? a. amount of sleep b. group b subjects c. memory d. group a subjects