why D but not C

@cassandra17er, The passage tells us that calcium carbonate neutralizes stomach acids but can increase the calcium level in the blood and thus impair kidney function, thus it is advisable to limit the dosage to half a gram. Moreover, just half a gram of it can stimulate the production of acid secretion. The problem with (C) as you pointed out is that we cannot infer what the net effect is at a dose of smaller than half a gram versus a much larger dose, especially considering this answer choice fails to specify what is a much larger dose. We can infer that this much larger dose is likely to increase the calcium level and stimulate the production of gastrin but a net result could still be a more effective acid neutralization versus a small dose. (D) on the other hand, is directly supported by the information in the passage saying that half a gram can trigger acid secretion and neutralize stomach acids at the same time. Notice that (D) avoids making this judgment on what the net result would be. Does this make sense? Let me know if you have any further questions.