For each of the following hypothetical scenarios, state whether selection or assignment is being described. Is the method of selection or assignment random? Explain your answer. 

a. A study of the services offered by counseling centers at Canadian universities studied 20 universities; every Canadian university had an equal chance of being in this study. 

b. In a study of phobias, 30 rhesus monkeys were either exposed to fearful stimuli or not exposed to fearful stimuli. Every monkey had an equal chance of being placed in either of the exposure conditions. 

c. In a study of cell phone usage, participants were recruited by including along with their cell phone bill an invitation to participate in the study. 

d. In a study of visual perception, 120 Introduction to Psychology students were recruited to participate.