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。
71. People in prehistoric times created paints by grinding materials such as plants and clay into power and then adding water. 71.史前的人们制造颜料是将植物和泥土等原料磨成粉末,然后加水。