sentence2_structure: This process<>takes<>the longest amount of time<>usually
sentence1: Such measurements on rocks of different ages provide a means of tracing the movements of continents and islands and ocean basins over geologic time, and the record of these movements shows great changes in the Earth's geography during its long history.
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?