The statement that is NOT a reason that most sharks must always keep swimming is:
2) they will get too cold, due to being cold-blooded.
Most sharks are actually classified as ectothermic, or "cold-blooded," meaning they do not regulate their body temperature internally, but many species of sharks can maintain a body temperature that is warmer than the surrounding water due to their unique physiological adaptations. Thus, while they must swim to keep water flowing over their gills for respiration and to prevent sinking, the cold-blooded aspect is not a primary reason for the need to keep swimming.