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问题:

Which of the following is true according to the passage? [A]Fluvaccinesnowmainlyus

Which of the following is true according to the passage?

[A] Flu vaccines now mainly use egg-based technology.

[B] A bird influenza has once circulated among humans.

[C] Safety can be greatly improved with cell-culture vaccines.

[D] Modern vaccine production methods are to replace egg-based methods.


  参考答案

正确答案:A

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[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.
The tone of the author in reporting the joint press conference this Monday is _____.
[A] astonished
[B] enthusiastic
[C] disappointed
[D] objective

[A] on [B] in [C] with [D] about