职称英语考试

【单选题】The GrandCanyonStanding on the rim of the GrandCanyon(大峡谷), gazing across this giant wound in theEarth’’s surface, a visitor might assume that the canyon had been caused by some ancient convulsion(震动). In fact, the events that produced the canyon, far from being sudden and catastrophic, simply add up to the slow and orderly process of erosion.Many millions of years ago, theColorado Plateau in the GrandCanyon area contained 1,000 more feet of rock than it does today and was relatively level. The additional material consisted of some 14 layered formations of rock. In the GrandCanyon region these layers were largely worn away over the course of millions of years. Approximately 65 million years ago the plateau s flat surface in the GrandCanyon area bulged upward from internal pressure, geologists refer to this bulging actions upwarding (弯曲上升) ; it was followed by a general elevation of the wholeColorado Plateau, a process that is still going on.As the plateau gradually rose, shallow rivers that winded across it began to run more swiftly and cut more definite courses. One of these rivers , located east of the upward, was the ancestor of theColorado.Another river system, called the Hualapai, flowing west of the upward, extended itself eastward by cutting back into the upward, it eventually connected with the ancientColorado and captured its waters. The new river then began to carve out the 277-mile-long trench that eventually became the GrandCanyon. Geologists estimate that this initial cutting action began no earlier than 10 million years ago.Since then, theCanyon forming has been cumulative. To the corrosive force of the river itself have been added other factors. Heat and cold, rain and snow, along with the varying resistance of the rocks, increase the opportunities for erosions. TheCanyon walls crumble, the river acquires a cutting tool. Tons of debris, rainfall running off the high plateau creates feeder streams that carreside canyons. Pushing slowly backward into the plateau, the side canyons expose new rocks, and the pattern of erosion continues. The passage mainly discusses______.
A、patterns of erosion in different mountain ranges
B．forces that made the GrandCanyon
C．the increasing pollution of theColorado River
D．the sudden appearance of the GrandCanyon

网考网参考答案：B
网考网解析：
第一段指出大峡谷的形成是由于缓慢有序的侵蚀形成的；第二段又说几百万年前大峡谷一带还是平面的，后来被逐渐侵蚀；第三段说由于地面隆起，便有了高原河流，也有了著名的大峡谷；最后一段又进一步说明了大峡谷的进一步形成是由于力的作用。因而本篇讨论的是形成大峡谷的各种力。故选B)。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>