This question examines the understanding of sentence structure and the function of specific phrases within a sentence. The correct answer identifies the phrase as providing a reason for the despair of patients, which in turn fuels the assisted-suicide debate. This is directly related to the main idea of the sentence. Option A is incorrect because the phrase is closely related to the main idea. Option C is incorrect as it misinterprets the phrase's meaning, which is about prolonging, not alleviating, suffering. Option D is incorrect because the phrase does not exemplify successful medical interventions but rather a consequence of modern medicine.