Icebergs—giant blocks of ice that float in the sea—come in many shapes, sizes, and colors. Some are deep blue or green. Some look like floating sculptures. Old icebergs that have been worn down by the weather sometimes look like pillars of ice. Usually, only about one-fifth of an iceberg appears above the surface of the water. The other four-fifths of the “berg” is hidden underwater, out of sight. Sometimes, an iceberg has what is called a “foot,” an extension completely underwater. These are especially dangerous for ships. It was an iceberg “foot” that sank the Titanic in 1912, killing 1,503 people. Which text structure is used?