听力原文： TUVALU, a tiny country in the Pacific Ocean, has asked for help as it fears it will be swallowed up by the sea. Storms and huge waves are a constant threat and none of Tuvalu's nine little islands is more than five meters above sea level. Salt water is already entering the country's drinking water supply, as well as damaging plants that produce fruit and vegetable. Without urgent help, the country's days are numbered. But Tuvalu is not the first place to face sinking into the sea. Venice, a historic city in Italy, best known for its canals, has sunk about 24 cm over the past 100 years. Experts say that it will have sunk another 20-50 cm by 2050. A century ago, St. Mark's Square, the lowest point in the city, flooded about nine times a year. Nowadays, it happens more than 100 times. While Venice is slowly sinking into the mud on which it stands. Tuvalu's rising sea level is caused by global warming. The average global temperatures also make water expand, so it takes up more space, causing the sea level to rise. The sea level has risen about 10-25 cm in the last 100 years. The main cause of global warming is human pollution. Through burning coal, oil and gas, people have been increasing the greenhouse gases in the atmosphere, such as CO2. This adds to the power of the greenhouse effect, making the planet even warmer. (30)