Fourth grade, the second volume, four exercises of Chinese group, 250 words.

Before, my father took me to Sea World. I saw all kinds of strange fish, including ray, naked-breasted eel, snake eel, jellyfish, squid, catfish, great white shark, porpoise, grouper, butterfly fish, stickleback, parrotfish and stickleback.

Among them, the great white shark is the most striking. Its body is streamlined, big and fierce, and its resistance is very strong. There is also an anticancer substance in it. If humans can extract it and reproduce it, people will not be afraid of the attack of cancer, and cancer will no longer become an "incurable disease".

After returning home, I leafed through books and looked for information about sharks. At first glance, it surprised me: sharks have lived in the ocean for more than 300 million years, with a speed of 70 kilometers per hour. When scientists examined the skin of deep-sea sharks under a microscope, they accidentally found that shark scales were fan-shaped and had small grooves. People used to think that the smoother the surface, the smaller the resistance. Scientists put hundreds of models at different angles, and tests show that the friction loss is 65,438+00% less than that of smooth surfaces. If this new discovery is applied to bionics, after improving the aircraft shell, the fuel consumption of each aircraft will be reduced by 350 tons per year. If the shell is installed on the passenger plane traveling around the world every year, the fuel consumption will reach billions of dollars, and the carbon dioxide and nitrogen oxides will be greatly reduced, thus improving the global greenhouse effect.

Nature is really a good teacher for human beings! People have learned a lot from nature and benefited from it. We should protect the natural and ecological environment!

There is a little turtle in my home, which is a little smaller than my fist. Its hard taupe back shell is semi-arched. Its head is triangular, probably to reduce the resistance of water. Its small eyes are round and bright, and there are two small nostrils at the front of its head, which is very interesting. Look at those four calves, short and thick, covered with tiny scales and with five small claws at the end.

Usually, the little turtle lies quietly in the water, sticking its head out of the water, motionless, and looks "quiet". But even if there is a slight movement, even footsteps, it will find it, and immediately retract its head, revealing only two small eyes and watching warily. After a long time, it will shake its neck and try to stick its head out bit by bit. How vigilant the little turtle is!

I don't think you will believe that this slow-moving and clumsy little guy can catch fish! But this is wrong.

Once, I fed a small turtle a few small crucian carp three or four centimeters long. Very interesting. As soon as the little fish was put into the pot, its neck, which had just been retracted, came out again, and two small eyes stared at the little fish. I wonder: can it catch small fish? This little fish is very clever, but it ... didn't expect the little turtle to be smarter. It didn't make a move, but lay there quietly, waiting for the opportunity. A few small fish didn't expect their natural enemies to be close at hand and still playing around. I held my breath and opened my eyes. Finally, a small fish swam to the little turtle. The little turtle caught up with him in a few steps and bit his head with his mouth open. The small fish didn't have a good meal until I thought it was "safe". I saw its neck stretched out, apparently swallowing small fish, and its two front legs were still swinging back and forth, as if exerting force. Look, how interesting!

However, if you disturb him while he is eating, he will immediately put down his food and put his head out of the water to "spy" before continuing his delicious meal. It can be seen that the little turtle will not relax his vigilance even when eating!

Anyone who knows a little about history knows Oracle Bone Inscriptions, right? In Shang dynasty, people once dug holes in tortoise shells and then burned them on fire. When these small holes burst into a "divination" shape, the fortune teller decided the good or ill luck, and then carved the prayer, result and divination date on a piece of Oracle Bone Inscriptions, which became the "Oracle Bone Inscriptions". Nowadays, people in the Yin Dynasty.

Not only that, the meat of the tortoise is edible, and the tortoise shell can be used as medicine.

It seems that the little turtle is not only smart and lovely, but also an animal that is very beneficial to human beings!