Read the following passage and mark the letter A, B, C, or D on your answer sheet to lớn indicate the correct answer to lớn each of the questions from 44 to lớn 50
If you go back far enough, everything lived in the sea. At various points in evolutionary history, enterprising individuals within many different animal groups moved out onto the land, sometimes even to lớn the most parched deserts, taking their own private seawater with them in blood and cellular fluids. In addition to lớn the reptiles, birds, mammals and insects which we see all around us, other groups that have succeeded out of water include scorpions, snails, crustaceans such as woodlice and land crabs, millipedes and centipedes, spiders and various worms. And we mustn’t forget the plants, without whose prior invasion of the land, none of the other migrations could have happened.
Moving from water to lớn land involved a major redesign of every aspect of life, including breathing and reproduction. Nevertheless, a good number of thoroughgoing land animals later turned around, abandoned their hard-earned terrestrial re-tooling, and returned to lớn the water again. Seals have only gone part way back. They show us what the intermediates might have been lượt thích, on the way to lớn extreme cases such as whales and dugongs. Whales (including the small whales we gọi dolphins) and dugongs, with their close cousins, the manatees, ceased to lớn be land creatures altogether and reverted to lớn the full marine habits of their remote ancestors. They don’t even come ashore to lớn breed. They bởi, however, still breathe air, having never developed anything equivalent to lớn the gills of their earlier marine incarnation. Turtles went back to lớn the sea a very long time ago and, lượt thích all vertebrate returnees to lớn the water, they breathe air. However, they are, in one respect, less fully given back to lớn the water than vãn whales or dugongs, for turtles still lúc lắc their eggs on beaches.
There is evidence that all modem turtles are descended from a terrestrial ancestor which lived before most of the dinosaurs. There are two key fossils called Proganochelys quenstedti and Palaeochersis talampayensis dating from early dinosaur times, which appear to lớn be close to lớn the ancestry of all modem turtles and tortoise. You might wonder how we can tell whether fossil animals lived in land or in water, especially if only fragments are found. Sometimes it’s obvious. Ichthyosaurs were reptilian contemporaries of the dinosaurs, with fins and streamlined bodies. The fossils look lượt thích dolphins and they surely lived lượt thích dolphins, in the water. With turtles it is a little less obvious. One way to lớn tell is by measuring the bones of their forelimbs.
Which of the following best serves as the main idea for the passage?