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(56) heavy as 204 kilograms. These turtles are found nesting（筑巢）along the coastline of more than 80 countries，with the largest nesting populations (57)in Costa Rica and Australia. Green sea turtles spend most of their lives underwater, (58) they can rest for up to five hours at a time before (59 )up for air. When active,they typically stay underwater for a few minutes and swim up to the surface to(60)air for a few seconds.Green sea turtles also bathe in the sun (61) land. Unlike most other sea turtles,adult green sea turtles eat primarily plant-based foods(62) of seaweed and sea grass. Scientists believe these green foods (63)the sea turtle's fat its green color. Similar to other sea turtles,green sea turtles travel long distances(64)their feeding grounds and their nesting sites,with recorded distances(65)than 2,600 kilometers.They have strong flippers（鳍形肢）that help them(66)in the water. Female green sea turtles leave the water in (67)to lay eggs on the beach and will choose the same nesting (68)as where they are born.A female will dig (69)a nest with her flippers and lay about 115 eggs.Then she'll cover the eggs (70)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(71 )at sea,where they feed on tiny animals and plants(72)live in the surface layer of the sea. As they grow older, the turtles move to  (73)waters along the coast,where they find sea grass to eat. Adult green sea turtles face many threats, primarily from humans,including injuries from passing boats,being(74)in fishing nets and pollution. Newly hatched sea turtles are also at(75)of being hunted by other animals as they move from their nests out to the sea.