Which of the following is characteristic of complex carbohydrates?

Complex carbohydrates are primarily characterized by their structure, which consists of long chains of monosaccharide molecules. These chains can vary in length and can consist of numerous glucose units or other sugar monomers linked together. This structure allows them to store energy more effectively compared to simple carbohydrates, which consist of just one or a few monosaccharides.

Option B highlights this fundamental aspect of complex carbohydrates, emphasizing their composition of many monosaccharide units. This characteristic is significant because it differentiates them from simpler carbohydrates, which are composed of fewer sugar molecules. Complex carbohydrates include substances like starch and glycogen, which are essential for energy storage in living organisms.

Other options do not accurately represent the nature of complex carbohydrates. They can indeed be broken down, which is vital for energy utilization. While some complex carbohydrates may have branched structures, this is not a defining characteristic of all complex carbohydrates, as others may be linear. The description of having a simple structure does not apply, as complexity signifies that they are indeed more intricate than simple carbohydrates.