OG4 阅读 Q45

Choice D is the best answer. According to lines 5-8("That... glass"), "That a powerful volcano erupted somewhere in the world, sometime in the Middle Ages, is written in polar ice cores in the form of layers of sulfate deposits and tiny shards of volcanic glass." The phrase "is written in" reinforces the idea that the polar ice caps contain evidence of the volcanic eruption, and that scientists can interpret this evidence by examining the "sulfate deposits and tiny shards of volcanic glass."
Choices A, B, and C are incorrect because the author does not use the phrase "is written in" to demonstrate the concept of the hands-on nature of the scientists' work, highlight the fact that scientists often write about their work, or underscore the sense of importance scientists have about their work.