As food travels through the digestive system, it is exposed to a variety of pH levels. The stomach has a pH of 2 due to the presence of hydrochloride acid (HCI), and the small intestine has a pH ranging from 7 to 9. HCI converts pepsinogen into pepsin, an enzyme that digests proteins in the stomach. Which of the following most likely happens to pepsin as it enters the small intestine.
A. it becomes inactive
B. It begins to replicate
C. Its shape changes to engulf large pepsin
D. Its activity increases to digest more proteins
