Identify the true statement. a. A deep-sea trench is a wedge-shaped mass of sediment scraped off a subducting plate as it slides under the overriding plate. b. Plate boundaries where subduction occurs are also called passive boundaries. c. Sea-floor spreading behind a volcanic island arc creates a small ocean basin called a back-arc basin or marginal sea. d. A spreading boundary is always in the middle of the ocean basin where it is located.