A new medication, drug A, is being developed for the treatment of peptic ulcer disease.  During initial testing, gastric acid secretion in experimental animals is stimulated by vagal stimulation, histamine infusion, or gastrin infusion.  Before the stimulus is administered, the animals are divided into 2 groups, one group receives pretreatment with drug A, and the second one serves as the control and is given an injection of an equivalent volume of normal saline.  The effects of the drug on hydrochloric acid (HCl) output by the stomach mucosa are recorded and shown in the graphs below.

Drug A is most similar to which of the following medications?

A 52-year-old postmenopausal woman comes to the office for evaluation of several months of episodic abdominal discomfort and nausea, especially after a fatty meal.  She has no past medical history and does not use tobacco, alcohol, or illicit drugs.  Her BMI is 33 kg/m2.  Physical examination shows a soft, nontender abdomen with normal bowel sounds.  Liver span is 8 cm.  Murphy sign is negative.  Abdominal x-ray reveals no calcifications, but abdominal ultrasound shows a small, non-obstructing gallstone.  The patient prefers nonoperative management.  Which of the following would best treat this patient’s condition?

A 42-year-old woman comes to the office due to a 2-month history of an intermittent burning sensation in her chest with an occasional simultaneous acidic taste at the back of her throat. The symptoms occur soon after she eats a meal. The patient has no shortness of breath, lightheadedness, nausea, vomiting, or weight loss. She has no other medical conditions. The patient has smoked a pack of cigarettes daily for the last 10 years but does not use alcohol. Family history is unremarkable. Vital signs are within normal limits. BMI is 32 kg/m2. Physical examination shows no abnormalities. Urine pregnancy test is negative. Smoking cessation is discussed, and a medication is prescribed for treatment of her symptoms. The patient returns in 2 weeks for a follow-up visit and reports near-complete resolution of her symptoms. Which of the following is the most likely mechanism of action of this drug?

A 42-year-old woman comes to the office due to frequent episodes of burning in her chest and small amounts of regurgitation after meals and at nighttime.  Medical history includes hypertension.  Vital signs are within normal limits.  BMI is 30 kg/m2.  There is no abdominal tenderness and the remainder of the physical examination is normal.  The patient shows the clinician an over-the-counter antacid that she has been taking to relieve her symptoms.  The preparation contains a combination of magnesium and aluminum hydroxide.  Which of the following is the most likely rationale for combining both mineral salts in this antacid preparation?