Q: What are complex carbohydrates composed of or characterized by?

Answer: (D) All of the above
Explanation: Complex carbohydrates are a type of carbohydrate that includes polysaccharides such as glycogen, cellulose, and starch. These molecules are composed of many glucose units linked together in long chains. This structural complexity allows them to serve various functions in the body, such as energy storage and providing structural support in plants. Therefore, all the options listed are correct descriptions of complex carbohydrates.