Answer:
Active transport
Explanation:
The text is most likely speaking about active transport, such as endocytosis and exocytosis, which is essentially the process in which a cell uses to consume larger particles/molecules and expose of them, respectively.
A. Immune system
It helps our bodies fight everything that comes in our path.
Pepsin is most active in acidic environments between 37 °C and 42 °C. Accordingly, its primary site of synthesis and activity is in the stomach (pH 1.5 to 2).