Why do athletes often eat lots of carbohydrates the day before a competition? carbohydrates provide lots of dietary fiber. carbohydrates provide lots of cellulose. carbohydrates give living things energy. carbohydrates build tissues in muscles?

The correct answer would be option C, Carbohydrates give living things energy.  

Explanation:  

All living things need food to get energy in order to perform the day to day activities. There are many sources of energy. Different types of food make up different sources of energy. There are many sources of energy like carbohydrates, fats, proteins, Vitamins, etc. Carbohydrates are the sugars, starches and fibers, that are present in foods like fruits, vegetables and dairy products. Carbohydrates are considered to be most effective way of providing the energy to the human body. So athletes use carbohydrates before competition in order to get a lot of energy so that they cannot run out of energy during the competition.