Refer to the Graphs Below

Refer to the graphs below.

Researchers wanted to determine if ideas about race affect our visual perception. In an experiment, white college students were asked to look at a screen with images of objects that were either crime-relevant (e.g., a handgun) or crime-irrelevant (e.g., a book) . For each object, the first image was so blurry it was unrecognizable. The image became progressively clearer across 40 different frames until the students were able to correctly identify it.
Before they began the task, they were shown a photo for 50 milliseconds. The photo was of a black face, a white face, or an abstract line drawing. These "flashes" were subliminal images, meaning that the students were not aware of having seen them. Researchers wanted to find out whether seeing a black or white face, even without being aware of it, influenced the students' ability to identify the objects.
-A hallmark of psychology as a science is critical thinking. What is a valid criticism of this perception experiment?

A) There was no need to show students an abstract line drawing.
B) It was unethical not to tell the students they were being shown subliminal images.
C) There might have been something about the faces used, apart from race, that influenced the students' perception of the images.
D) Researchers should have shown students only "crime-irrelevant objects."