TOEFL Listening: TPO-TOEFL阅读TPO - 04Y0VSQ4049N4EB6N$

The author mentions "spreading ridges", "subduction zones", and "transform faults" in order to A. illustrate that the boundaries of tectonic plates are neat, thin lines B. explain why some tectonic plates carry islands or continents while others form the seafloor C. explain the complex nature of the edges of tectonic plates D. provide examples of areas of tectonic plates where little geologic action occurs