Dr Elder Was Interested in the Way People Recognize Objects

Dr. Elder was interested in the way people recognize objects as members of categories. For example, what makes us recognize a dog as being a dog and not a cat? More specifically, he was curious as to whether people think about categories in a more complex way if they contemplate an "opposite" category first. For example, does a person think differently about the category of "southern" if they first think about the category of "northern"? He is also curious as to whether people categorize differently if they are exposed to category members compared with generating category members. Dr. Elder has four groups of participants (with 30 people in each group) . In Group A, participants were told to cut out pictures of dogs and cats from magazines. In Group B, participants were told to cut out pictures of just dogs from magazines. In Group C, participants were told to draw pictures of cats and dogs. In Group D, participants were told to draw pictures of just dogs. After doing this for 30 minutes, participants in all groups were asked to list the attributes that define the "dog" category. Having a higher number of attributes listed was considered to be an indication of thinking about the category in a more complex way. The results of his study are below.

In Dr. Elder's study, how many possible main effects exist?

A) 1
B) 2
C) 3
D) 4