Which of these is purposefully changed during a scientific investigation? a test variable (independent variable) b outcome variable (dependent variable) c control group d hypothesis

The independent variable is the only one that can change. Outcome variable depends on the test variable, so it isn't purposely changed. The control group isn't changed, because then it wouldn't be a control. And if you changed the hypothesis, you would basically be cheating and saying you knew what would happen before the experiment.

A. Test variable (independent variable)!

Explanation:

both anaerobic and aerobic respiration use glucose (or other carbohydrates), proteins and lipids to produce atp and nadh. cell uses those energy molecules, obtained from food and   breaks them down during the chemical reactions of respiration. in anaerobic respiration, nadh is regenerated to nad+ by enzymes lactate dehydrogenase (lactate is produced, e.g. in muscle cells) or by alcohol dehydrogenase where ethanol is produced (alcohol fermentation), while in aerobic respiration, electrons from nadh are deposited in the mitochondria to regenerate nad+ (electron transport chain. anaerobic respiration produces 2 atp per molecule of glucose compared to aerobic respiration where about 38 atp molecules are produced.