Answer:
(a).concentrated lactic acid and that of NAD+.
(b).use of the response of NAD+ and lactic acid in absence of vitamin treatment as the CONTROL.
Explanation:
To understand this question and be able to solve this question efficiently we have to understand the concept of "respiration''. But, the short and the most simple answer to the question above can be found in the first statement of the question.
The electron transport chain include the cycle that occurs during glycolysis, fermentation and the transformation of NAD+ to form NADH and vice versa.
In the research, the dependent variable is the concentrated lactic acid and that of NAD+.
In order to increase the validity of the experiment, the Researcher can make use of the response of NAD+ and lactic acid in absence of vitamin treatment as the CONTROL.