sentence2_structure: This process<>takes<>the longest amount of time<>usually
sentence1: Rift basins that form along the margins of continents during the tectonic opening of an ocean basin may contain unusually rich concentrations of oil if the timing of geologic events was appropriate, or may contain virtually no energy resources if the timing was inappropriate.
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?