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Bacteria multiply fastest in moderate warmth, where conditions are warm enough to fuel cell division but not so hot they’re killed. That makes the 70–125°F range the time when growth is most rapid, so foods left in this zone can quickly become unsafe. At fridge temperatures (32–40°F) or below freezing (0–32°F), growth slows or stops, which is why refrigeration and freezing help preserve food. At high heat (140–160°F), most bacteria are killed or cannot multiply, which is why cooking and hot-holding temperatures are used for safety. So, the best answer is the warm, moderate range because it represents where bacteria grow most quickly.