GRE閱讀高頻機經原文：冰川沉積物

想必大家在備考gre考試的時候，最喜歡的就是吸取新鮮的考試真題，這樣對自己的能力也是一個考驗，最能檢驗自己目前的能力在什麼水平，今天小編爲大家帶來的就是GRE閱讀高頻機經原文：冰川沉積物!

GRE閱讀高頻機經原文：冰川沉積物

14. 冰川沉積物

Tills are commonly classi?ed according to the perceived process of deposition. However, it is increasingly recognised that this classi?cation, which is mainly based on macroscopic ?eld data, has severe limitations. At the same time the concept of the deforming glacier bed has become more realistic as a framework for discussing tills and their properties, and this (tectonic) concept is irreconcilable with the existing (depositional) till classi?cation scheme. Over the last 20 years large thin sections have been used to study tills, which has provided new insights into the textural and structural properties of tills. These results have revolutionised till sedimentology as they show that, in the main, subglacial tills possess deformational characteristics. Depositional properties are rare.

Based on this new insight the process of subglacial till formation is discussed in terms of glacier/ice sheet basal velocity, clay, water and carbonate content and the variability of these properties in space and time. The end result of this discussion is: till, the deforming glacier bed. To distinguish subglacial till from depositional sediments the term ‘tectomict’ is proposed. Within the single framework of subglacial till as the deforming glacier bed, many textural, structural and geomorphological features of till beds can be more clearly and coherently explained and understood.

　　GRE閱讀高頻機經原文及答案：雲和氣候變化預測

15. 雲和氣候變化預測 1996年04月北美 D9604

As of the late 1980’s, neither theorists nor large-scale computer climate models could accurately predict whether cloud systems would help or hurt a warming globe. Some studies suggested that a four percent increase in stratocumulus clouds over the ocean could compensate for a doubling in atmospheric carbon dioxide, preventing a potentially disastrous planetwide temperature increase. On the other hand, an increase in cirrus clouds could increase global warming.

That clouds represented the weakest element in climate models was illustrated by a study of fourteen such models. Comparing climate forecasts for a world with double the current amount of carbon dioxide, researchers found that the models agreed quite well if clouds were not included. But when clouds were incorporated, a wide range of forecasts was produced. With such discrepancies plaguing the models, scientists could not easily predict how quickly the world’s climate would change, nor could they tell which regions would face dustier droughts or deadlier monsoons.

15.1. The author of the passage is primarily concerned with

(A) confirming a theory

(B) supporting a statement

(C) presenting new information

(D) predicting future discoveries

(E) reconciling discrepant findings

15.2. It can be inferred that one reason the fourteen models described in the passage failed to agree was that

(A) they failed to incorporate the most up-to-date information about the effect of clouds on climate

(B) they were based on faulty information about factors other than clouds that affect climate

(C) they were based on different assumptions about the overall effects of clouds on climate

(D) their originators disagreed about the kinds of forecasts the models should provide

(E) their originators disagreed about the factors other than clouds that should be included in the models

15.3. It can be inferred that the primary purpose of the models included in the study discussed in the second paragraph of the passage was to

(A) predict future changes in the world’s climate

(B) predict the effects of cloud systems on the world’s climate

(C) find a way to prevent a disastrous planetwide temperature increase

(D) assess the percentage of the Earth’s surface covered by cloud systems

(E) estimate by how much the amount of carbon dioxide in the Earth’s atmosphere will increase

15.4. The information in the passage suggests that scientists would have to answer which of the following questions in order to predict the effect of clouds on the warming of the globe?

(A) What kinds of cloud systems will form over the Earth?

(B) How can cloud systems be encouraged to form over the ocean?

(C) What are the causes of the projected planetwide temperature increase?

(D) What proportion of cloud systems are currently composed of cirrus of clouds?

(E) What proportion of the clouds in the atmosphere form over land masses?

答案：B C A A

GRE閱讀高頻機經原文及答案：Supernova

16. Supernova D 89-12

Astronomers observe a supernova that is dimmer than expected because of dust screening，If a supernova (the explosion of a massive star) triggered star formation from dense clouds of gas and dust, and if the most massive star to be formed from the cloud evolved into a supernova and triggered a new round of star formation, and so on, then a chain of star-forming regions would result. If many such chains were created in a differentially rotating galaxy, the distribution of stars would resemble the observed distribute in a spiral galaxy.

This line of reasoning underlies an exciting new theory of spiral-galaxy structure. A computer simulation based on this theory has reproduced the appearance of many spiral galaxies without assuming an underlying density wave, the hallmark of the most widely accepted theory of the large-scale structure of spiral galaxies. That theory maintains that a density wave of spiral form sweeps through the central plane of a galaxy, compressing clouds of gas and dust, which collapse into stars that form a spiral pattern.