To investigate people's ability to divide their attention between two different tasks, college students were asked to listen to a passage of expository prose and at the same time to inspect a set of photographs, unrelated to the passage, that were projected one by one at a rapid rate. At the end of the dual-task presentation, the students were tested both for their memory of the passage and their memory of the photographs. To establish a baseline for this dual-task condition, the same students also were tested for their memory when each of the component tasks was presented alone. The following graph shows the results. <image 1> In a study of the effectiveness of divided attention, it is most important that the experimental design include
['a counterbalance of the order in which participants are tested in the baseline and dual-task conditions', 'a consistent order in which participants are tested in the baseline and dual-task conditions', 'an equal number of men and women as participants', 'verification that participants believe themselves capable of dividing attention']