Hello, 

I think I would just use the "Call" method with an appropriate step page to be calling the right class.

You can use the when rule in the activity step and use continue when when it's true and skip step when it's false.

What is the relationship between the three Work classes - Candidate, BenefitsEnrollment and PayrollSetup? Something tells me your activities are created in the wrong classes.

The short answer is you would need an instance of BenefitsEnrollment as a page on the clipboard. The name of that page is referenced as your Step Page at which point you use "Call ActivityB". Same principle applies with Activity C.

Note that your "When" configurations for any Activity step also use the Step Page as the context, so you would need to use "Primary" here to refer to your existing Candidate instance (which is the context for the call to your "Test" Activity) in 'When' expressions where the Step Page references a different page on the clipboard (i.e. your instance of BenefitsEnrollment or PayrollSetup)

Reply back if this isn't addressing what you were asking.

The activity in other class may also be called using 'Call ClassName.ActivityName' instruction. For example, in your case you can call Activity B by using instruction as 'Call TGB-HRApps-Work-BenefitsEnrollment.Activity B' and in same way you can call Activity C using 'Call TGB-HRApps-Work-PayrollSetup.Activity C' from Activity Test.