All nuts on clevises must be _________.

The correct answer emphasizes that all nuts on clevises must be secure to ensure safety and integrity in operations involving sling loads. When nuts are hand tight and taped, this indicates a temporary solution which can risk failure if the load is subjected to movement or stress. The process of securing materials like nuts firmly and perhaps with additional measures such as tape helps prevent any loosening during the operation, which is crucial when dealing with heavy or dynamic loads.

While taking into account the other options, it is essential to recognize their implications. For instance, loosely fitted nuts can lead to operational failures due to vibrations or shifting of the load. Similarly, while torquing to specification is crucial in many cases, it's not solely enough if the securing methods do not apply in the particular context. Lastly, ensuring all components are clean and rust-free is important for maintaining the integrity of the equipment over time but does not directly address the immediate security requirement of the nuts during operations. Thus, the choice that highlights the need for a more immediate and practical fastening method is the most relevant and appropriate in this situation.