Green sea turtles are reptiles (爬行动物). They are {#blank#}1{#/blank#} (find) throughout the world's seas. They are probably the oldest animals {#blank#}2{#/blank#}the Earth. Their ancestors(祖先) used to walk on land, and then went back {#blank#}3{#/blank#}the sea many million years ago. They watched dinosaurs go missing. Although they are endangered animals, the number of them is{#blank#}4{#/blank#}(rise). Green sea turtles are cold-blooded and they breathe air. They each have a hard shell like nearly all turtles. Many land turtles are able to take their heads back into their shells for {#blank#}5{#/blank#}(protect). Green sea turtles cannot do this, and their heads will be out at all times. Their shells are {#blank#}6{#/blank#}(light) in weight than those which live on land. When green sea turtles swim, they will come out of the sea every few {#blank#}7{#/blank#} (minute) to take a breath.{#blank#}8{#/blank#} when they sleep, they can remain in water for two hours without taking a breath. Green sea turtles seem to grow very {#blank#}9{#/blank#} (slow). Adult green sea turtles can weigh about 500 pounds. Green sea turtles live in the ocean {#blank#}10{#/blank#} most of their adult lives.