Verification of truth – "A factory must have ____." Identify the necessary component.

Introduction / Context:
The prompt asks for a requirement that applies to factories in general, not only to specific eras or industries. We interpret “labour” broadly as human workers (including supervisory/technical staff).

Given Data / Assumptions:

• Factories are places of production/processing.
• Some factories are highly automated.
• Not all factories have chimneys (non-smokestack industries), nor run exclusively on electricity in all historical contexts.

Concept / Approach:
Even automated plants require human personnel for operation, oversight, safety, maintenance, logistics, and quality control. Thus, some level of labour is indispensable.

Step-by-Step Solution:

Verification / Alternative check:
Legal/safety regimes require responsible human operators; fully “lights-out” plants still maintain staff for monitoring and intervention.

Why Other Options Are Wrong:
They are contingent on industry or organizational structure, not definitional.

Common Pitfalls:
Equating common modern features (electricity) with logical necessities.

Final Answer:
Labour