"which form of carbohydrate is the only one used by the body in its natural form? "

glucose

Glucose is the only monosaccharide that can used in its natural form because it's the body’s preferred energy source.
The body processes most carbohydrates ingested into glucose, to be used immediately, as a source of energy, or to be stored in muscle or liver cells as glycogen for later use.

Wikipedia aswell can be used to solve the following questions