A researcher would like to study the effect of eating breakfast on a cognitive function. Volunteers are recruited through the study by posting flyers on campus. He randomly assigns subjects to two groups, one told to eat before participating in the study and one asked to eat breakfast following the study, however, he suspects whether or not the person typically eats breakfast affects this relationship (their typical breakfast habits). In order to address this, what should he do prior to assigning subjects to experimental groups?

a.
Cluster on typical breakfast habits

b.
Randomly assign subjects to typical breakfast habits and do a multifactor experiment

c.
Sample from each strata, typical breakfast eater and not

d.
Block on typical breakfast habits