Alot of microbes such as e. coli can be used in modern scientific research because

a) e. coli has genetic and metabolic similarity with other organisms
b) e. coli is totally different from any other species
c) e. coli is not a disease-causing organism
d) e. coli is a disease-causing organism

A) E. coli has genetic and metabolic similarity with other organisms

Explanation:

In most scientific researches scientists try to make an analogy to understand the cause and effect of the events. They use also microbes such as E.coli because E.coli, a kind of bacteria has genetic and metabolic similarity with other organisms.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.