What process must happen before this process depicted below?

two pyruvate molecules are converted to two lactic acid molecules. two nadh molecules are converted to two nad+ molecules in the process.

fermentation
cellular respiration
krebs cycle
glycolysis

The correct answer is Glycolysis.

Explanation:

Glycolysis is the partial breakdown of glucose into two pyruvate molecules. This reaction occurs in the cytoplasm of the cell. There is a net generation of 2 NADH and 2 ATP in the process of glycolysis. This pathway occurs in both aerobic and anaerobic conditions.

In anaerobes, it is called fermentation in which two pyruvate is converted into lactate by converting 2 NADH produced during glycolysis into 2 NAD⁺. The release of NAD⁺ than supplied to glycolysis again so that glycolysis keep running.

                       Glucose →  2 pyruvate → 2 lactate              

Therefore, the glycolysis process must take place before two pyruvate molecules are converted to two lactic acid molecules.  

they deliver oxygen to the blood

cell regulation is conducted by special proteins.