What Did the Researchers, Who Identified the Hawthorne Effect, See

What did the researchers, who identified the Hawthorne effect, see as evidence that employee performance was influenced by something other than the physical work conditions?

A) Any change in a variable, such as lighting levels, led to an improvement in productivity; this was true even when the change was negative, such as a return to poor lighting.
B) Employees who believed they were under observation performed the same as employees who did not believe they were under observation.
C) Employees who knew they were being observed called in sick more often than employees who did not know they were being observed.
D) Managers who told their subordinates they were under observation received more complaints than other managers.