Botany, the study of plants, plays a strange role in the history of human knowledge. For many thousands of years it was one field about which humans had little knowledge. It is impossible to know today just what our Stone Age Ancestors knew about plants, but from what we can observe of preindustrial societies that still exists, a detailed learning of plants and their properties（特征）must be very ancient. This is reasonable. Plants are the basis of the food pyramid for all living things, even for other plants. They have always been greatly important to the good of peoples, not only for food, but also for clothing, weapons, tools, medicines, housing, and a great many other purposes. Tribes（部落）living today in the woods of the Amazon recognize hundreds of plants and know many properties of each. To them botany, as such, has no name and is probably not even recognized as a special branch of knowledge at all.
Unfortunately, the more industrialized we become the farther away we move from direct relation with plants, and the less clear our knowledge of botany grows. Yet everyone comes unconsciously on a surprising amount of botanical knowledge, and few people will fail to recognize a rose or an apple. When our New Stone Age ancestors, living in the Middle East about 10 000 years ago, discovered that certain grasses could be harvested and their seeds planted for richer production the next season, the first great step in a new connection of plants and humans was taken. Grains were discovered and from them flowed the marvel of agriculture: planted crops. From then on, humans would increasingly take their living from the controlled production of a few plants, rather than getting a little here and a little there from many varieties that grew wild and the collected knowledge of tens of thousands of years of experience and close relations with plants in the wild would begin to disappear.
67. Which of the following assumptions（假设）about early humans is expressed in the passage?
A. They probably had wide knowledge of plants.
B. They clearly divided knowledge into separate fields
C. They did not enjoy the study of botany.
D. They placed great importance on ownership of property.
68.According to the passage, why has general knowledge of botany decreased?
A. People no longer value plants as a useful resource.
B. Botany is not recognized as a special branch of science.
C. Research is unable to keep up with the increasing number of plants.
D. Direct relation with a variety of plants has decreased.
69. In paragraph 2, the underlined word “marvel” is closest in meaning to _____.
A. edge B. sign C. beginning D. wonder
70. According to the passage, what was the first great step toward the practice of agriculture?
A. The invention of agriculture tools and machines.
B. The development of a system of names for plants.
C. The discovery of grasses that could be harvested and replanted.