4. 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. It's shape changes to engulf large proteins.
D. It's activity increases
to digest more proteins.