Final answer:
Trainees are not to be assigned to final control positions during known adverse weather conditions to ensure safety and efficiency of air traffic control.
Step-by-step explanation:
Trainees shall not be assigned to final control positions (precision, ASR, or PALS) during adverse weather conditions that are known. The correct answer to the question is c. Known user. This pertains to the forecasted or already occurring weather conditions which are definitively known at the time of the assignment. Since weather conditions can significantly affect the complexity of air traffic control, it is crucial that only fully qualified controllers handle final control positions during such conditions. Trainees, therefore, should not be assigned to these roles to ensure the safety and efficiency of air navigation services during known adverse weather conditions.