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  3. EI Nino is the term used for the period when sea surface temperatures are above normal off the South American coast along the eq

EI Nino is the term used for the period when sea surface temperatures are above normal off the South American coast along the eq

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问题     EI Nino is the term used for the period when sea surface temperatures are above normal off the South American coast along the equatorial Pacific, sometimes called the Earth’s heartbeat, and is a dramatic but mysterious climate system that periodically rages across the Pacific.
    El Nino means "the little boy" or "the Christ child" in Spanish, and is so called because its warm current is felt along coastal Peru and Ecuador around Christmas. But the local warming is just part of an intricate
set of changes in the ocean and atmosphere across the tropical Pacific, which covers a third of the Earth’s circumference. Its intensity is such that it affects temperatures, storm tracks and rainfall around the world.
    Droughts in Africa and Australia, tropical storms in the Pacific, torrential rains along the Californian coast and lush greening of Peruvian deserts have all been ascribed to the whim of EI Nino. Until recently it has been returning about every three to five years. But recently it has become more frequent--for the first time on record it has returned for a fourth consecutive year--and at the same time a giant pool of unusually warm water has settled down in the middle of the Pacific and is showing no signs of moving.
    Climatologists don’t yet know why, though some are saying these aberrations may signal a worldwide change in climate. The problem is that nobody really seems sure what causes the EI Nino to start, and what makes some stronger than others. And this makes it particularly hard to explain why it as suddenly started behaving so differently.
    In the absence of EI Nino and its cold counterpart, La Nina, conditions in the tropical eastern Pacific are the opposite of those in the west: the east is cool and dry, while the west is hot and wet. In the east, it’s the winds and currents that keep things cool. It works like this. Strong, steady winds, called trade winds, blowing west across the Pacific drag the surface water along with them. The varying influence of the Earth’s rotation at different latitudes, known as the Coriolis effect, causes these surface winds and water to veer towards the poles, north in the northern hemisphere and south in the southern hemisphere. The surface water is replaced by colder water from deeper in the ocean in a process known as upwelling.
    The cold surface water in mm chills the air above it. This cold dense air cannot rise high enough or water vapor to condense into clouds. The dense air creates an area of high pressure so that the atmosphere over the equatorial eastern Pacific is essentially devoid of rainfall.
We can learn from the beginning of the text that EI Nino is a phenomenon ______
选项 A、which occurs in some areas other than the Pacific.
B、whose effects direct winds to move to the poles.
C、which human activities are chiefly responsible for.
D、whose causes remain a mystery to human beings.
答案D
解析 题干问：“从本文的开头可以得知厄尔尼诺是一种什么现象?”D“其原因对人类来说仍然相当神秘”正确，第1自然段作者明确使用了“mysterious”这个词来说明这一自然现象，而这个思想在第4自然段继续得以加强和巩固。而选项A“发生在太平洋以外的某些地区”，与原文的意思相反。选项B“其效果让风往极向运动”，而厄尔尼诺没有造成风往极向运动的现象，造成风往极向运动的是第5自然段的“科里奥利力”。选项C“广人类活动直接导致了这种现象”，常识告诉我们人类的活动可能对这种现象有辅助作用，但文章开头和本文并没有直接提出人类的活动直接导致了厄尔尼诺现象。
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