Answer:
<u><em>sample </em></u>
Explanation:
A sample can be described as some people or objects which are under observation by a researcher. The sample taken can be from a certain area and can help to depict results for experiments performed on the particular area. A sample is a small part which reflects the results for the whole community or area. A sample is taken by researchers for analysis. As Dr. Wong took his students for an experiment on conformity, hence the children will be the sample for the experiment. 
 
        
             
        
        
        
Make a graph and find out 
        
             
        
        
        
D. You group like things, typing isn't really used in that sense, classifying is another word for grouping, but cataloging is and after action list