A hiker is climbing up a steep path. Halfway up, he finds the muscles in his legs are experiencing a burning and aching sensation. What is the most likely
cause of these symptoms?

A. He has a large buildup of lactate in his muscles.
B. The Krebs cycle is producing too much waste.
C. He has eaten too much sugar.
D. The sun was overheating his muscles.

A. He has a large buildup of lactate in his muscles.

Explanation:

Ideally, our body cells, via the process of aerobic cellular respiration, need oxygen to break down glucose. However, during rigorous activities or exercises, oxygen can become unavailable for use. In this case, the body cells switch to use another way of cellular respiration, which is FERMENTATION.

This fermentation causes a build up of lactic acid/lactate (its byproduct) in the cells of the muscles being used, which physically causes a burning and aching sensation just as the case of this hiker. The climbing of the steep path is causing causing the fast usage of oxygen in his cells.

nucleus

would be most reasonable answer tbh

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".