What does the quoted word 'fundamental' mean in the following sentence?

The correct answer is 'D: Basic.' In this context, 'fundamental' means basic or essential, referring to the core or foundational dissimilarity between the two medications. Choice A, 'Appropriate,' is incorrect as it does not reflect the meaning of 'fundamental' in this sentence. Choice B, 'Underlying,' is incorrect because although it is related, it does not capture the primary or essential nature of the difference being discussed. Choice C, 'Dosage,' is unrelated to the meaning of 'fundamental' and does not align with the context of the sentence.