The Primary Lesson to Be Learned from the Lawsuit Brought

The primary lesson to be learned from the lawsuit brought by Microsoft's temporary workers in the 1990s is that:

A) it is safest legally to hire temp workers through  a temporary staffing agency
B) employers must provide benefits to all of their employees
C) companies that use temp workers will often be deemed joint employers of those workers
D) employers cannot arbitrarily exclude some employees from benefit plans by labeling them as temporary workers