Which factor(s) help slow down biological activity and preserve food?

The correct choice is all of the above because each of these factors can influence the biological activity in food preservation in unique ways. High temperatures can indeed accelerate biological activity, particularly in the growth of microorganisms; however, when food is heated beyond certain thresholds, it can kill or deactivate harmful microorganisms, thus contributing to preservation.

Salt acts as a preservative by drawing moisture out of foods and creating an environment where bacteria struggle to grow. It dehydrates microbial cells and inhibits their metabolic activities, thus slowing down spoilage. This is why salt curing is a long-standing method of food preservation.

High moisture levels typically promote microbial growth, so while it might initially seem contradictory in the context of preservation, it also plays a role. When combined with salt or other preservatives, managing moisture levels can help achieve an optimal balance that preserves food while preventing spoilage.

Therefore, all of these factors, in different ways and contexts, contribute to slowing down biological activity and ultimately help in preserving food.