Section_ⅠWarming Up & Reading - Pre­reading

　　There are a great many plants and animals that live under the sea. Do you know something about sea turtles? And how they live under the sea? Please read the following passage to get the answers.

　　Sea turtles are sometimes referred to as "marine turtles"， referencing the fact that they have adapted to living primarily in the marine environment. All seven living species of sea turtles are endangered, and conservation efforts all over the world are attempting to prevent the extinction of sea turtles. The loss of sea turtles would not just be a blow to biodiversity: sea turtles are also important for the health of the world's oceans.

　　Like other turtles, sea turtles have a hard shell into which they can retreat. Their front legs have adapted into a flipper­like (鳍状的) form which allows them to swim rapidly and efficiently, and their bodies are slightly flattened to reduce resistance in the water. Some sea turtles can also use their flippers for climbing.

　　The sea turtle has developed a respiratory (呼吸的) system which allows it to dive and stay underwater for as long as five minutes. Depending on the turtle's level of activity and stress, it may need to surface soon for air. Sea turtles breathe in explosively, filling their lungs with enough air to supply them during dives.

　　Sea turtles feed on other marine life and seagrass, a flowering plant which is widespread in the world's oceans. They can be found in every ocean except the Arctic. Sea turtles are especially vulnerable (易受伤的) during egg laying, since many are slow and unhandy on land, and the eggs may be broken by careless walkers or viewed as a tasty snack by numerous predators. Once the eggs hatch, the young make their way to the ocean and begin their water life.

　　The smallest sea turtles reach a length of around 30 inches, while the largest can exceed six feet. Sea turtles live for up to 80 years, and once they reach their maturity, they are difficult for predators to kill, thanks to their hard shells. They are easily vulnerable, however, to trawling and a variety of other human activities, along with changes in the marine environment such as coral bleaching (珊瑚白化) and nutrient pollution.

Warming Up