第一篇 先进的探测方法
原文回顾： 一些先进的科技和地理知识的运用可以帮助分析和测定一些历史上的情况，每一段都讲了不同的探测方法。
相关背景学习：Rossi X-ray Timing Explorer
The Rossi X-ray Timing Explorer (RXTE) is a satellite that observed the time structure of astronomical X-ray sources, named after Bruno Rossi. The RXTE has three instruments—the Proportional Counter Array, the High-Energy X-ray Timing Experiment (HEXTE), and the All Sky Monitor. The RXTE observed X-rays from black holes, neutron stars, X-ray pulsars and X-ray bursts. It was funded as part of the Explorer program, and is sometimes also called Explorer 69.
RXTE was launched from Cape Canaveral on 30 December 1995 on a Delta rocket, has an International Designator of 1995-074A and a mass of 3200 kg.
Observations from the Rossi X-ray Timing Explorer have been used as evidence for the existence of the frame-dragging effect predicted by the theory of general relativity. RXTE results have, as of late 2007, been used in more than 1400 scientific papers.
In January 2006, it was announced that Rossi had been used to locate a candidate intermediate-mass black hole named M82 X-1. In February 2006, data from RXTE was used to prove that the diffuse background X-ray glow in our galaxy comes from innumerable, previously undetected white dwarfs and from other stars' coronae. In April 2008, RXTE data was used to infer the size of the smallest known black hole.
RXTE ceased science operations on 3 January 2012.
NASA scientists said that the decommissioned RXTE would re-enter the Earth's atmosphere "between 2014 and 2023".
第二篇 威尼斯缺水问题
原文回顾：威尼斯缺饮用水的问题。由于污染的问题，威尼斯本身缺少淡水，所以缺少饮用水就成了大问题。
相关背景学习：Causes of limited fresh water
There are many causes of the apparent decrease[citation needed] in our fresh water supply. Principal amongst these is the increase in population through increasing life expectancy, the increase in per capita water use and the desire of many people to live in warm climates that have naturally low levels of fresh water resources.[citation needed] Climate change is also likely to change the availability and distribution of fresh water across the planet:
"If global warming continues to melt glaciers in the polar regions, as expected, the supply of fresh water may actually decrease. First, fresh water from the melting glaciers will mingle with salt water in the oceans and become too salty to drink. Second, the increased ocean volume will cause sea levels to rise, contaminating freshwater sources along coastal regions with seawater”.
The World Bank adds that the response by freshwater ecosystems to a changing climate can be described in terms of three interrelated components: water quality, water quantity or volume, and water timing. A change in one often leads to shifts in the others as well. Water pollution and subsequent eutrophication also reduces the availability of fresh water.
Also, there is an uneven distribution of fresh water. While some countries have an abundant supply of fresh water, others do not have as much. For example, Canada has 20% of the world's fresh water supply, while India has only 10% of the world's fresh water supply, even though India's population is more than 30 times larger than that of Canada. A reason for the uneven distribution of fresh water supply may be the differences in climate. For example, in some countries in Africa, the frequent lack of rain has led to insufficient water supply for irrigation. This has affected agriculture and has led to a shortage of food for the people.
第三篇 青蛙的叫声
原文回顾： 雄性青蛙叫声的变化对雌性青蛙的吸引和影响，另外不同青蛙的叫声对于敌人的吸引和影响。
相关背景学习：Animals Sound
Territory sounds
These are sounds, calls, or audible signals made by any one species to its own or any other species, establishing boundaries so like or unlike species will not transgress those boundaries.
Male baboons make sounds heard for miles by other baboons, communicating to those other male baboons, the territory of that male baboon. The strength, volume, and timbre, inherent in that "call", determine whether or not rival males attempt to invade that male baboon's territory.
They do this to make them sound impressive and then to attract the female to them.
Courtship and/or mate attracting sounds
These are sounds made by the male baboon to attract females to his territory for courtship and mating. Again, the strength, quality, and timbre of those sounds, often determine the ability of that species to attract females for reproduction. These mating calls, often low and guttural, are the main criteria, used by the female baboon to determine which male she mates with.
词汇题：
oblige=force
ensure=guarantee
henceforth=from past to now
excavation=dig out
substantial=considerable
incite=stimulate
alteration=modified
in preference to=more than
constituent=component
characteristic=typical
outweigh=exceed
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