The correct answer is C) Never. The reason for this is that the crane boom should never be raised so high that it hits the stops, as this can cause damage to the crane and potentially lead to a dangerous situation. Crane operators are trained to avoid this scenario and to keep the boom within its safe operating range at all times, regardless of the load or the materials being lifted. Hitting the boom stops can put excessive stress on the crane's components and increase the risk of the crane tipping or collapsing. The other answer choices are incorrect because A) allowing the boom to hit the stops based on the load limit is unsafe, B) there is no valid reason to purposefully hit the boom stops, and D) the materials being lifted should not factor into the decision to avoid hitting the stops.