63.人类骨骼有二百多块骨头组成，住些骨头石油坚韧而相对缺乏弹性的，被称为韧带的结蒂组连在一起。

64. The pigmentation of a pearl is influenced by the type of oyster in which it develops and by the depth, temperature, and the salt content of the water in which the oyster lives.

64.珍珠的色泽受到作为其母体牡蛎种类及牡蛎生活水域的深度，温度和含盐度的制约。

65. Although mockingbirds superbly mimic the songs and calls of many birds, they can nonetheless be quickly identified as mockingbirds by certain aural clues.

65.尽管模仿鸟学很多种鸟的鸣叫声惟妙惟肖，但人类还是能够依其声音上的线索很快识别它们。

66. Not only can walking fish live out of water, but they can also travel short distances over land.

66.鲇鱼不仅可以离开水存活，还可以在岸上短距离移动。

67. Scientists do not know why dinosaurs became extinct, but some theories postulate that changers in geography, climate, and sea levels were responsible.

67.科学家不知道恐龙为何绝种了，但是一些理论推断是地理，气候和海平面的变化造成的。

68. The science of horticulture, in which the primary concerns are maximum yield and superior quality, utilizes inFORMation derived from other sciences.

68.主要目的在于丰富和优质的农艺学利用了其他科学的知识。

69. Snow aids farmers by keeping heart in the lower ground levels, thereby saving the seeds from freezing.

69.雪对农民是一种帮助，因为它保持地层土壤的温度，使种子不致冻死。

70. Even though the precise qualities of hero in literary words may vary over time, the basic exemplary function of the hero seems to remain constant.