Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: Monosaccharides A monosaccharide is a monomer of carbohydrates. Five monosaccharides are important in the body. Three of these are the hexose sugars, so called because they each contain six atoms of carbon. These are glucose, fructose, and galactose, shown in Figure 2.18a. The remaining monosaccharides are the two pentose sugars, each of which contains five atoms of carbon. They are ribose and deoxyribose, shown in Figure 2.18b. Answer: carbon
Glucose, fructose, and galactose are hexose sugars, which contain six atoms of what element?