Final answer:
The best indicator that the treatment with propranolol has been effective in a patient with cirrhosis and esophageal varices is the patient's stools testing negative for occult blood, indicating that there is no active variceal bleeding.
Step-by-step explanation:
A patient with cirrhosis and esophageal varices treated with propranolol is best indicated to have effective treatment if their stools test negative for occult blood (option c). Propranolol, a beta-blocker, is used in this case to reduce the pressure within the veins that can lead to variceal bleeding. Esophageal varices are prone to bleeding due to the high pressure in the portal venous system caused by cirrhosis. Propranolol reduces the risk of bleeding by lowering blood pressure and heart rate, thus decreasing blood flow to the esophageal varices. While a normal blood pressure (option b) and apical pulse rate (option d) indicate that the propranolol is having its expected physiological effects, the absence of occult blood in the stool is the most direct indicator that the varices are not bleeding, which is the primary risk and concern with esophageal varices.