Answer: B) chitin Explanation: Many carbohydrates contain one or more modified monosaccharide units that have had one or more groups replaced or removed.   Chitin is one of many naturally occurring polymers. It is one of the most abundant natural materials in the world. Over time it is bio-degradable in the natural environment. Its breakdown may be catalyzed by enzymes called chitinases, secreted by microorganisms such as bacteria and fungi, and produced by some plants.   Chitin is composed of repeating units of N-acetylglucosamine, a nitrogen-containing form of glucose.