One Technique Researchers Have Used to Directly Test Whether Demand

One technique researchers have used to directly test whether demand characteristics are influencing the results of mental scanning tasks is

A) to scan the participant's brain and to see if areas of the brain associated with imagery are active.
B) to explicitly tell participants to not pay attention to any cues that the experimenter may be giving.
C) to ask participants to make judgments about spatial layout as if they were looking at an actual picture.
D) to ask participants to make judgments about spatial layout without ever mentioning the idea of "imagery."