Green sea turtles(海龟) are the world' s largest species of hard-shelled sea turtle. While most individuals weigh about 136 to 181 kilograms, some can be【C1】______ heavy as 204 kilograms. These turtles are found nesting(筑巢) along the coastline of more than 80 countries with the largest nesting populations【C2】______ in Costa Rica and Australia. Green sea turtles spend most of their lives underwater,【C3】______ they can rest for up to five hours at a time before【C4】______ up for air. When active, they typically stay underwater for a few minutes and swim up to the surface to【C5】______ air for a few seconds. Green sea turtles also bathe in the sun【C6】______ land. Unlike most other sea turtles, adult green sea turtles eat primarily plant-based foods【C7】______ of seaweed and sea grass. Scientists believe these green foods【C8】______ the sea turtle's fat its green color. Similar to other sea turtles, green sea turtles travel long distances【C9】______ their feeding grounds and their nesting sites, with recorded distances【C10】______ than 2,600 kilometers. They have strong flippers (鳍形肢) that help them【C11】______ in the water. Female green sea turtles leave the water in【C12】______ to lay eggs on the beach and will choose the same nesting【C13】______ as where they were born. A female will dig【C14】______ a nest with her flippers and lay about 115 eggs. Then she'll cover the eggs【C15】______ sand and return to the sea. After about two months the babies will use a special "egg tooth" to break their shells and hatch(孵化) from their eggs. The first few years of a green sea turtle' s life are spent【C16】______ at sea, where they feed on tiny animals and plants【C17】______ live in the surface layer of the sea. As they grow older, the turtles move to【C18】______ waters along the coast, where they find sea grass to eat. Adult green sea turtles face many threats, primarily form humans, including injuries from passing boats, being【C19】______ in fishing nets and pollution. Newly hatched sea turtles are also at【C20】______ of being hunted by other animals as they move from their nests out to the sea.