Which of the following statements best describes the structure of carbohydrates?
1) Carbohydrates are composed of a glycerol group and three fatty acid tails.
2) Carbohydrates are composed of a hydrophilic phosphate head and two hydrophobic fatty acid tails.
3) Carbohydrates are composed of repeating units of amino acids that are bonded together.
4) Carbohydrates are composed of one or more monosaccharides, which are small ringed structures that have carbon, hydrogen, and oxygen in a 1:2:1 ratio.