OG2 阅读 Q43

Choice C is the best answer. In the first paragraph, the author identifies the natural phenomenon “internal waves” (line 3，“these...the”), and explains why they are important: “internal waves are fundamental parts of ocean water dynamics, transferring heat to the ocean depths and bringing up cold water from below” (lines 7-9,"hidden...below").
Choices A, B, and D are incorrect because they do not identify the main purpose of the first paragraph, as that paragraph does not focus on a scientific device, a common misconception, or a recent study.