A group of 220 volunteers is first separated into 6 groups, labeled A to F, based upon age and weight such that these qualities are similar within each group. The age and weight of the volunteer is initially measured. Within each group, participants are randomly assigned to either undergo the new exercise program or undergo a conventional exercise program. In addition, the daily calorie intake is set to a particular amount, either low, moderate or high, and maintained at that level for the duration of the program. At the end of six months, the percentage of weight lost is measured for each unit and the results are collected and compared. This testing procedure is an example of a:

a. completely randomized design experiment
b. randomized block design experiment
c. matched pairs experiment