Understanding the Multiple Choice, Single Answer Task in PTE Academic, UKVI & Core

B-15 broke off from the Ross Ice Shelf in Antarctica. It was the largest iceberg ever documented, with a surface area of more than 4,200 square miles — more than twice the size of the state of Delaware. After it started breaking up, the largest of its pieces, B-15a, drifted along the coast of Antarctica, lingered on a shallow seamount, and collided with an ice tongue, before running aground and breaking again. Late in 2007, the largest remaining chunk floated out into the South Pacific where, in the warmer water, it began to disintegrate.For the whole of the next year, the ocean was noisier than usual. All the way up past the equator, 4,350 miles or so away from where B-15a broke apart, hydrophones that scientists from the National Oceanic and Atmospheric Administration (NOAA) had suspended underwater were picking up strange signals. Another set of hydrophones, this one in the Juan Fernández Islands, off the coast of Chile, picked up the noise, too, even louder. When the scientists used the two sets of data to determine the source of the noise, they found the most likely culprits: B-15a and C-19a, another giant iceberg.Twenty years ago, not so long before B-15 broke off from Antarctica, “we didn’t even know that icebergs made noise,” says Haru Matsumoto, an ocean engineer at NOAA who has studied these sounds. But in the past few years, scientists have started to learn to distinguish the eerie, haunting sounds of iceberg life — ice cracking, icebergs grinding against each other, an iceberg grounding on the seafloor — and measure the extent to which those sounds contribute to the noise of the ocean. While they’re just now learning to listen, the sounds of ice could help them understand the behavior and breakup of icebergs and ice shelves as the poles warm up.

Greenhouse gases arise from a wide range of sources and their increasing concentration is largely related to the compound effects of increased population, improved living standards, and changes in lifestyle. From a current base of 5 billion, the United Nations predicts that the global population may stabilize in the twenty-first century between 8 and 14 billion, with more than 90 percent of the projected increase taking place in the world’s developing nations. The associated activities to support that growth, particularly to produce the required energy and food, will cause further increases in greenhouse gas emissions. The challenge, therefore, is to attain a sustainable balance between population, economic growth, and the environment.

Large earthquakes or volcanic eruptions can cause tsunamis, which in Japanese means “wave in the harbor”. Tsunamis move very fast, up to 500 miles per hour. Upon reaching shallower waters, they start to decelerate but increase in height. A tsunami can become a wall of water that can reach more than 10 meters high as it approaches the shore. The height depends on two factors: the depth of coastal waters and the shape of the beach. If the wave reaches dry land, it can cause considerable damage and inundate vast areas.