Part B

　　Directions:

　　In the following article, some sentences have been removed. For Questions 41-45, choose the most suitable one from the lish A-G to fit into each of the numbered blank. There are two extra choices that do not fit in any of the gaps. Mark your answers on ANSWER SHEET 1. (10 points)

　　Until about two million years ago Africa’s vegetation had always been controlled by the interactions of climate; geology, soil, and groundwater conditions; and the activities of animals. The addition of humans to the latter group, however, has increasingly rendered unreal the concept of a fully developed “natural” vegetation—i.e., one approximating the ideal of a vegetational climax. (41). Early attempts at mapping and classifying Africa’s vegetation stressed this relationship: sometimes the names of plant zones were derived directly from climates. In this discussion the idea of zones is retained only in a broad descriptive sense.

　　(42). In addition, over time more floral regions of varying shape and size have been recognized. Many schemes have arisen successively, all of which have had to take views on two important aspects: the general scale of treatment to be adopted, and the degree to which human modification is to be comprehended or discounted.

　　(43). Quite the opposite assumption is now frequently advanced. An intimate combination of many species—in complex associations and related to localized soils, slopes, and drainage—has been detailed in many studies of the African tropics. In a few square miles there may be a visible succession from swamp with papyrus, the grass of which the ancient Egyptians made paper and from which the word “paper” originated, through swampy grassland and broad-leaved woodland and grass to a patch of forest on richer hillside soil, and finally to juicy fleshy plants on a nearly naked rock summit.

　　(44). Correspondingly, classifications have differed greatly in their principles for naming, grouping, and describing formations: some have chosen terms such as forest, woodland, thorn-bush, thicket, and shrub for much of the same broad tracts that others have grouped as wooded savanna (treeless grassy plain) and steppe (grassy plain with few trees). This is best seen in the nomenclature, naming of plants, adopted by two of the most comprehensive and authoritative maps of Africa’s vegetation that have been published: R. W. J. Keay’s Vegetation Map of Africa South of the Tropic of Cancer and its more widely based successor, The Vegetation Map of Africa, compiled by Frank White. In the Keay map the terms “savanna” and “steppe” were adopted as precise definition of formations, based on the herb layer and the coverage of woody vegetation; the White map, however, discarded these two categories as specific classifications. Yet any rapid absence of savanna as in its popular and more general sense is doubtful.

　　(45). However, some 100 specific types of vegetation identified on the source map have been compressed into 14 broader classifications.

　　[A] As more has become known of the many thousands of African plant species and their complex ecology, naming, classification, and mapping have also become more particular, stressing what was actually present rather than postulating about climatic potential.

　　[B] In regions of higher rainfall, such as eastern Africa, savanna vegetation is maintained by periodic fires. Consuming dry grass at the end of the rainy season, the fires burn back the forest vegetation, check the invasion of trees and shrubs, and stimulate new grass growth.

　　[C] Once, as with the scientific treatment of African soils, a much greater uniformity was attributed to the vegetation than would have been generally accepted in the same period for treatments of the lands of western Europe or the United States.

　　[D] The vegetational map of Africa and general vegetation groupings used here follow the White map and its extensive annotations.

　　[E] African vegetation zones are closely linked to climatic zones, with the same zones occurring both north and south of the equator in broadly similar patterns. As with climatic zones, differences in the amount and seasonal distribution of precipitation constitute the most important influence on the development of vegetation.

　　[F] Nevertheless, in broad terms, climate remains the dominant control over vegetation. Zonal belts of precipitation, reflection latitude and contrasting exposure to the Atlantic and Indian oceans and their currents, give some reality to related belts of vegetation.

　　[G] The span of human occupation in Africa is believed to exceed that of any other continent. All the resultant activities have tended, on balance, to reduce tree cover and increase grassland; but there has been considerable dispute among scholars concerning the natural versus human-caused development of most African grasslands at the regional level.

　　答案

　　41.F 42.A 43.C 44.G 45.D

　　总体分析

　　本文是一篇介绍非洲植被研究的科普性文章。

　　第一段：在非洲植被的图形绘制及其分类中很早就重视了植被与气候之间的密切关系。

　　第二段：随着人们对非洲植物的了解增加，对植物的命名、分类和绘制图形变得更加具体，许多有关植物区域的规划也被提出来。

　　第三段：现在人们更强调非洲植物的多样性而非一致性。

　　第四段：学者们对非洲草地发展的原因，对植物群系的命名、归类以及描述的原则都存在分歧。

　　第五段：介绍现在非洲植被图谱对植物的归类法。

　　[A] 随着人们对植物了解的增加，对植物的命名、分类和绘制图形也更加具体。

　　[B] 在高降水量的地区，大草原的植被因周期性的火灾而得以保存。

　　[C] 非洲东部植被被认为有很大的一致性。

　　[D] 现在的植物图谱及植物分类都受怀特图谱的影响。

　　[E] 影响植被发展的几个因素。

　　[F] 叙述了影响植被的气候因素。

　　[G] 学者们对于导致非洲草地发展的原因，存在很大的分歧。