The correct answer is A) log the reason for not completing the drill. According to the regulations, if a required drill is not completed on a mobile offshore drilling unit (MODU), the master or person in charge must document the reason for not completing the drill in the vessel's log. This is the appropriate action, as it ensures the incident is properly recorded and can be reviewed by the relevant authorities if necessary. The other options are incorrect because they either require additional actions (B), or involve reporting the incident to the wrong authorities (C and D), which is not the correct procedure in this case.