The correct answer is C) the entire practical demonstration has been successfully completed and personally observed by the licensed officer. This is correct because the licensed officer designated to certify a trainee's performance of a practical demonstration should only sign off once they have personally observed the entire demonstration being completed successfully. The licensed officer needs to witness the full performance to ensure the trainee has demonstrated the required skills and competencies. Signing off prematurely, such as after only a portion of the demonstration or after a pre-brief, would not provide sufficient validation of the trainee's abilities. The other options are incorrect because they do not require the licensed officer to personally observe the full practical demonstration. Option A would allow another officer to witness the performance, while options B and D do not necessitate observing the entire demonstration.