The correct answer is D. time spent by workers on their job.
Idle time is time spent by workers on their job that is not productive. It can be caused by a number of factors, such as waiting for materials, equipment, or instructions, or by poor work methods. Idle time can lead to lost productivity, increased costs, and employee dissatisfaction.
Option A is incorrect because it refers to time spent by workers in a factory. This time may or may not be productive, depending on the worker’s activities.
Option B is incorrect because it refers to time spent by workers in an office. This time may or may not be productive, depending on the worker’s activities.
Option C is incorrect because it refers to time spent by workers off their work. This time is not considered idle time, as it is not time spent on the job.