Key Interlocking in Electrical Power Systems

Can Someone explain the below question and answer:

A new double-ended low-voltage substation has a commonly used key interlock system. That system consists of an identical lock on each main breaker and the tie breaker. While confirming that the system works correctly you observe that all three locks have keys in them. Based on your knowledge of key interlocking practices, which of the following is the MOST correct with regard to this situation?

The answer was: If the keys are identical, the system can only work as designed if one of the keys is removed from the substation.

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Manufacturer will usually ship new equipment with spare keys. These keys are to be removed and held in a safe place in case copies need to be made. Extra keys are a huge safety hazard because they allow the system to be bypassed as designed.

Thanks for your explanation. Any reference to read about key interlocking in Electrical Systems?

Here are some resources to get you started: