sentence2_structure: This process<>takes<>the longest amount of time<>usually
sentence1: it provides evidence for the long lifespan of proto-Pacific ocean basins, and therefore of potentially immense areas of oceanic crust that must have disappeared by subduction beneath the North American continent in Paleozoic and Mesozoic times.
sentence2: This process usually takes the longest amount of time: an ocean basin forms between two continents.
question: Which of the following processes usually takes the longest amount of time?