A (crude) way to do this would be to create a numeric pass-in variable (myrand)
Assign it a random integer value between 1 and N where N is the number of CBC exercises you have.
You can do this by putting
[% SetValue(myrand,RandNum(999,1,N)) %]
in the footer of an early question.
Then use Skip Logic to determine which of the N CBC exercises a person sees, based on their value of myrand.
myrand=1 people see CBC 1 only
myrand=2 people see CBC 2 only
myrand=N people see CBC N only
Use “Generate Data” from the Test menu to send simulated respondents through the survey and then check that people only see one CBC exercise.
Sorting the data by myrand will make that easier to see if you are checking this visually (safer to check non-visually, especially if N is large)