What is mentioned in relation to the use of chains in a robot?

The correct choice states that robots must not reduce the working length of chains. This rule is essential in ensuring the effective transmission of power and movement within the robot's mechanisms. Reducing the working length of the chains could lead to mechanical issues, such as insufficient tension or improper gearing, which would compromise the robot's functionality. Maintaining the proper working length ensures that the chains operate as intended, providing reliable performance during competitions.

The other considerations regarding chains, such as the use of extra-long chains, visibility through color, or the necessity of constant movement, may not align with the fundamental requirement that focuses specifically on maintaining the chain's effective operational length in relation to the robot's design and functionality. This highlights that stability and performance come first when it comes to the use of chains in robotics.