Evaluations for input

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) a counterbalance of the order in which participants are tested in the baseline and dual-task conditions

(B) a consistent order in which participants are tested in the baseline and dual-task conditions

(C) an equal number of men and women as participants

(D) verification that participants believe themselves capable of dividing attention

Answer with the option's letter from the given choices directly. No punctuation.