Why does the author include the information that "Glaciers grind bedrock into fine sediment, which is carried by streams flowing from the melting ice"? A. To give a reason why heavily sedimented braided streams are common in glacial environments B. To explain why some mountain streams deposit most of their sediment in a fan-shaped mound C. To identify the most common source of sediment in arid and semiarid mountainous regions D. To help explain why glacial sediment decreases the gradient and velocity of steep mountain streams