Answer:
Oxaloacetate
Step-by-step explanation:
Throughout the citric acid cycle, in the matrix of the mitochondria, the 4 carbon molecule is transformed (through the addition and removal of carbon atoms) and ultimately regenerated before the beginning of another cycle. During this transformation of oxaloacetate, some intermediate products are of a lower energy level than their predecessors hence making the process energetically favorable. The energy difference is capture is energy molecules such as NADH. FADH₂, and ATP.