During strenuous exercise, glucose is changed into,
A) Starch
B) Glycogen
C) Lactic Acid
D) Pyruvic Acid

Hint:Glucose is the most important energy source for all the cells in the body and acts as a strong foundation for the larger molecules like glycoproteins.

Complete answer:
Let us go through the options carefully,
-Option A: Starch is usually excess glucose which is manufactured by the green plants and stored. When required it breaks down into simple constituents in the presence of certain enzymes which then provides the nutrients for cell growth. So, this option is not the correct one for this question.

-Option B: Glycogen is the excess form of glucose which is stored in the liver and muscles of the animals and is used only when required or when insufficient glucose is consumed. This conversion is not only restricted to a strenuous exercise situation and usually happens in aerobic situations and is therefore not the correct option.

-Option C: Lactic acid is produced from glucose during the process of anaerobic respiration where the cells produce energy in the absence of oxygen. During strenuous exercise, this process is common due to a rapid breathing action and when aerobic mechanisms seize. The lactate can build up in the muscles causing discomfort and disturbances in different metabolic pathways. Therefore, this is the correct option.

-Option D: Pyruvic acid is the middle product between catabolism and anabolism and is a key acid present in all the living cells. It is a very important constituent in many metabolic pathways like glycolysis and Kreb’s cycle. This is not the correct option as it's not really related to the question.

Therefore, the correct answer is option (C) Lactic Acid.

Note:Some underlying body conditions can increase the buildup of lactate in the muscles or decrease the ability to remove the extra lactate from the body which might lead to lactate acidosis.