Answer: "Employees" is the simple subject.
Step-by-step explanation:
A simple subject is the main word in a subject, without any modifiers that describe it. In order to determine the simple subject in a sentence, we should just ask ourselves who is the performer of the action in the sentence. In this case, the simple subject is the word ''employees'', while the complete subject (simple subject + the modifiers) is ''the employees at the factory."