老托福阅读100篇-练习阅读最好的材料.docx

智课网TOEFL备考资料老托福阅读100篇-练习阅读最好的材料 摘要： 不少考生来电咨询想要下载老托福阅读100篇的内容，今天小编花费了一定量的时间和精力，不服众望，下面就随着小编来了解下老托福阅读100篇的部分内容吧! 无论你基础差，或者基础好，练习阅读最好的材料-老 托福 阅读100篇,你的必备托福精华资料，这些资料对于学习好的学生和学习差的学生都是必不可少的。 Swimming Machines (OG Practice Set 6) Tunas, mackerels, and billfishes (marlins, sailfishes, and swordfish) swim continuously. Feeding,courtship, reproduction, and even rest are carried out while in constant motion. As a result, practically every aspect of the body form and function of these swimming machines is adapted to enhance their ability to swim. Many of the adaptations of these fishes serve to reduce water resistance (drag). Interestingly enough,several of these hydrodynamic adaptations resemble features designed to improve the aerodynamics of high-speed aircraft. Though human engineers are new to the game, tunas and their relatives evolved theirhigh-tech designs long ago. Tunas, mackerels, and billfishes have made streamlining into an art form. Their bodies are sleek and compact. The body shapes of tunas, in fact, are nearly ideal from an engineering point of view. Most species lack scales over most of the body, making it smooth and slippery. The eyes lie flush with the body and do not protrude at all. They are also covered with a slick, transparent lid that reduces drag. The fins are stiff, smooth, and narrow, qualities that also help cut drag. When not in use, the fins are tucked into special grooves or depressions so that they lie flush with the body and do not break up its smooth contours. Airplanes retract their landing gear while in flight for the same reason. Tunas, mackerels, and billfishes have even more sophisticated adaptations than these to improve their hydrodynamics. The long bill of marlins, sailfishes, and swordfish probably helps them slip through the water. Many supersonic aircraft have a similar needle at the nose. Most tunas and billfishes have a series of keels and finlets near the tail. Although most of their sca