One important element of a "key control policy" is:

Comprehensive Detailed Explanation:

A core element of an effective key control policy is ensuring accountability for all keys. This includes maintaining logs, conducting regular audits, and verifying that issued keys are returned or accounted for. This reduces the risk of unauthorized access and is fundamental in access control strategies.

A and C are arbitrary numeric limits and not standard policy practice.

D may be part of policy but is not as critical as ongoing accountability.