戴尔美语练功坊 托福阅读实力测验试题(6/20日)
WATER IN THE DESERT
WATER IN THE DESERT
Rainfall is not completely absent in desert areas, but it is highly
variable. An annual rainfall of four inches is often used to define the
limits of a desert. The impact of rainfall upon the surface water and
groundwater resources of the desert is greatly influenced by landforms.
Flats and depressions where water can collect are common features,
but they make up only a small part of the landscape.
Arid lands, surprisingly, contain some of the world's largest river
systems, such as the Murray-Darling in Australia, the Rio Grande in
North America, the Indus in Asia, and the Nile in Africa. These rivers
and river systems are known as "exogenous" because their sources lie
outside the arid zone. They are vital for sustaining life in some of the
driest parts of the world. For centuries, the annual floods of the Nile,
Tigris, and Euphrates, for example, has brought fertile silts and water
to the inhabitants of their lower valleys. Today, river discharges are
increasingly controlled by human intervention, creating a need for
international river-basin agreements. The filling of the Ataturk and
other dams in Turkey has drastically reduced flows in the Euphrates,
with potentially serious consequences for Syria and Iraq.
The flow of exogenous rivers varies with the season. The desert
sections of long rivers respond several months after rain has fallen
outside the desert, so that peak flows may be in the dry season.
This is useful for irrigation, but the high temperatures, low humidity,
and different day lengths of the dry season, compared to the normal
growing season, can present difficulties with some crops.
Regularly flowing rivers and streams that originate within arid
lands are known as "endogenous." These are generally fed by
groundwater springs, and many issue from limestone massifs, such as
the Atlas Mountains in Morocco. Basaltic rocks also support springs,
notably at the Jabal Al-Arab on the Jordan-Syria border.
(A)■ Endogenous Rivers often do not reach the sea but drain into
inland basins, where the water evaporates or is lost in the ground.
(B)■ Most desert streambeds are normally dry, but they occasionally
receive large flows of water and sediment. (C)■
Deserts contain large amounts of groundwater when compared
to the amounts they hold in surface stores such as lakes and rivers.
(D)■ But only a small fraction of groundwater enters the hydrological
cycle-feeding the flows of streams, maintaining lake levels, and being
recharged (or refilled) through surface flows and rainwater. In recent
years, groundwater has become an increasingly important source of
freshwater for desert dwellers. The United Nations Environment
Program and the World Bank have funded attempts to survey the
groundwater resources of arid lands and to develop appropriate
extraction techniques. Such programs are much needed because in
many arid lands there is only a vague idea of the extent of
groundwater resources. It is known, however, that the distribution
of groundwater is uneven, and that much of it lies at great depths.
Groundwater is stored in the pore spaces and joints of rocks and
unconsolidated (unsolidified) sediments or in the openings widened
through fractures and weathering. The water-saturated rock or
sediment is known as an "aquifer". Because they are porous,
sedimentary rocks, such as sandstones and conglomerates, are
important potential sources of groundwater. Large quantities of
water may also be stored in lime stones when joints and cracks have
been enlarged to form cavities. Most limestone and sandstone
aquifers are deep and extensive but may contain ground waters that
are not being recharged. Most shallow aquifers in sand and gravel
deposits produce lower yields, but they can be rapidly recharged.
Some deep aquifers are known as " fossil waters." The term
" fossil " describes water that has been present for several thousand
years. These aquifers became saturated more than 10, 000 years ago
and are no longer being recharged.
Water does not remain immobile in an aquifer but can seep out
at springs or leak into other aquifers. The rate of movement may be
very slow: in the Indus plain, the movement of saline (salty) ground
waters has still not
reached equilibrium after 70 years of being tapped. The mineral
content of groundwater normally increases with the depth, but even
quite shallow aquifers can be highly saline.
1. Which of the following statements about annual rainfall can be
inferred from paragraph 1?
(A) Flat desert areas receive more annual rainfall than desert areas
with mountains.
(B) Areas that receive more than four inches of rain per year are
not considered deserts.
(C) Many areas receive less than four inches of annual rainfall, but
only a few are deserts.
(D) Annual rainfall has no impact on the groundwater resources
of desert areas.
2. The word " drastically " in the passage is closest in meaning to
(A) obviously
(B) torpidly
(C) swiftly
(D) severely
3. In paragraph 2, why does the author mention the Ataturk and other
dams in Turkey?
(A) To contrast the Euphrates River with other exogenous rivers
(B) To illustrate the technological advances in dam building
(C) To argue that dams should not be built on the Euphrates River
(D) To support the idea that international river-basin agreements
are needed
4. According to paragraph 2, which of the following is true of the
Nile River?
(A) The Nile's flow in its desert sections is at its lowest during the
dry season.
(B) The Nile's sources are located in one of the most arid zones of
the world.
(C) The Nile's annual floods bring fertile silts and water to its lower
valley.
(D) The Nile's periodic flooding hinders the growth of some crops.
5. Paragraph 5 supports all of the following statements about the
groundwater in deserts EXCEPT:
(A) The groundwater is consistently found just below the surface
(B) A small part of the groundwater helps maintain lake levels
(C) Most of the groundwater is not recharged through surface water
(D) The groundwater is increasingly used as a source of freshwater
6. According to paragraph 6, which of the following statements about
aquifers in deserts is TRUE?
(A) Water from limestone and sandstone aquifers is generally
better to drink than water from sand and gravel aquifers.
(B) Sand and gravel aquifers tend to contain less groundwater than
limestone or sandstone aquifers.
(C) Groundwater in deep aquifers is more likely to be recharged
than groundwater in shallow aquifers.
(D) Sedimentary rocks, because they are porous, are not capable
of storing large amounts of groundwater.
7. According to paragraph 6, the aquifers called fossil waters
(A) contain fossils that are thousands of years old
(B) took more than 10, 000 years to become saturated with water
(C) have not gained or lost any water for thousands of years
(D) have been collecting water for the past 10,000 years
Answers:
1. 根据第一段, 关于年度降雨量可以推论出?
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