Im not sure if this was a mutiple choice, but i would say the sun or water. I'll explain both
Most living things need sunlight to grow like plants or farm crops and sun provides what it needs to grow and that dosent just benifit the plants it benifits us as well in order to stay healthy and fit you need vegetables and the sun helps provide that. The sun dosent just give you vegatables, In some places in order for cheese or some meat even it is a long process the meat or cheese goes through which involves sitting in the sun for hours
Now, as far as water goes its pretty self explanitory water keep us alive but it keeps animals alive and well without animal what will people eat