Final answer:
Bismuth subsalicylate (Pepto-Bismol) acts as an adsorbent by binding to diarrhea-causing bacteria and facilitating their excretion (option D).
Step-by-step explanation:
Bismuth subsalicylate, commonly known as Pepto-Bismol, is an antidiarrheal medication that serves several functions within the gastrointestinal tract. One of its major mechanisms of action is as an adsorbent, where the substance binds to pathogens in the gut, such as bacteria causing diarrhea, and helps to facilitate their excretion from the body. Specifically, this would correspond to option D: Binding to diarrhea-causing bacteria for excretion. It is important to mention that while this is one mechanism, bismuth subsalicylate also has other effects such as decreasing gastrointestinal motility and decreasing gastric secretions, which collectively contribute to its antidiarrheal properties.