Cells enter a futile substrate cycling during which increased intracellular glucose overwhelms the TCA cycle. As a result, non-oxidative glucose metabolism producing .

Explanation: Reciprocal regulation is intended to prevent concurrent activity in two closely parallel pathways, as represented by gluconeogenesis and glycolysis. These pathways include potential futile cycles, which would simply waste ATP if allowed to run freely.

the answer is definitely c.

the answer is:  

line graphs show patterns in data with variables that change over time; whereas, circle graphs show data as parts out of a whole (such as out of 100%).