C. From carbon dioxide in the atmosphere
I think it is the second answer, sorry if it is wrong/didn’t help.
<span>Pepsin is an enzyme that breaks down proteins into amino acids in the stomach (where the pH is 1-3). Pepsin needs to be in an acidic environment to be activated. The optimum temperature is between 30 oC and 40 oC because the average human body temperature is 37 oC. The optimum pH is the acidic one because your stomach has an acidic pH.</span>
