Which of the following is classified as a complex carbohydrate?

Starch is classified as a complex carbohydrate because it is composed of numerous glucose molecules linked together in a branched or unbranched structure. This arrangement allows it to serve as an energy storage form for plants. Complex carbohydrates, such as starch, are polysaccharides, which means they consist of multiple sugar units. They tend to be digested more slowly than simple carbohydrates, leading to a more gradual release of glucose into the bloodstream, which is beneficial for maintaining stable energy levels.

In contrast, the other options represent simple carbohydrates or disaccharides. Glucose and fructose are monosaccharides, which are the simplest form of carbohydrates consisting of single sugar units. Sucrose, on the other hand, is a disaccharide made up of glucose and fructose linked together. These simpler forms are quickly metabolized by the body compared to starch. Therefore, starch stands out as the only complex carbohydrate among the given choices.