Which lettered box could represent the rock conglomerate?

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.

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.

i think its both a and b