Question

【题目】根据短文理解，选择正确答案。
How the Grand Canyon (大峡谷) was created remains one of the geology's greatest mysteries. Some evidence suggests that the process was a gradual one in which the Colorado River (which runs through the canyon) slowly cut deeper and deeper into the ground over millions of years. But volcanic rock samples taken from the canyon now suggest that the canyon was down-cut instead.
Down-cutting is when a flood of water rushes over a landscape (地形) with enough force to cut deeply into the ground and leaves behind a canyon. Such a flood is usually released when a natural or man-made dam (堤坝) bursts.
Robert Webb, a research geologist, says natural dams seem to have formed and broken across the Colorado River several times during the last million years. The dams were built when lava(熔岩) from the eruptions of nearby volcanoes flowed into the river. The lava hardened into hard rocks and blocked the river, causing it to back up and form a lake. Each time the lake grew so huge that it broke the rock dam, releasing a flash flood that furthered the down-cutting process and deepened the canyon.
Down-cutting is not just an earthly event. Satellite photos sent back from Mars suggest that the process has happened there, too, say many other researchers.
The photos, taken by the Mars Global Surveyor, indicate that an enormous lake existed on Mars 3.5 billion years ago. The lake spilled into a large nearby hole. One edge of the hole broke, releasing a flash flood that quickly carved out a grand canyon.
The existence of down-cutting on Mars is just one more piece of evidence that the cold, dry planet was once warm and wet.
（1）In the past, deep canyons were believed to have formed _______.
A.as a result of a sudden break of volcanoes
B.due to river flows over millions of years
C.owing to the burst of artificial dams
D.thanks to our ancestors' creative work
（2）According to the passage, which of the following statements is TURE?
A.Several volcanoes broke out on Mars directly creating grand canyons.
B.Several great lakes existed on the upper parts of the Colorado River.
C.People built high dams on the upper parts of the Colorado River.
D.The Colorado River crossed the Grand Canyon to form down-cutting.
（3）From the last three paragraphs we learn that _______.
A.there are great lakes on Mars
B.there are active volcanoes on Mars
C.there might be cities on Mars
D.there might be life on Mars
（4）The passage can be titled as _______.
A.Lakes on Earth and Mars
B.The Cause of Lake Formation
C.The Force of Dam Breaking
D.Canyons—Results of Flood Cutting

Answer 1

【答案】
（1）B
（2）B
（3）D
（4）D
【解析】本文作者认为大峡谷的形成是洪水下切侵蚀造成的，主要是上游的湖泊泛滥下切侵蚀造成了峡谷，文章还介绍了在火星也有这种现象。

⑴细节理解。从文章第一段的句子：Some evidence suggests that the process was a gradual one in which the Colorado River (which runs through the canyon) slowly cut deeper and deeper into the ground over millions of years.可知，一些证据表明深深的峡谷据相信是由于几百万年的河流冲刷造成的，所以答案是B。

⑵细节理解。从文章第三段的句子：The lava hardened into hard rocks and blocked the river, causing it to back up and form a lake.可知，熔岩形成坚硬的岩石，阻挡了河流，使河的上游形成湖泊，所以答案是B。

⑶细节理解。从文章最后一段的句子The existence of down-cutting on Mars is just one more piece of evidence that the cold, dry planet was once warm and wet.可知，火星上流水侵蚀地貌的存在证明了火星上原来是温暖湿润的气候，也就是适宜生命存活，所以答案是D。

⑷主旨大意。从文章的内容和第二段的句子Down-cutting is when a flood of water rushes over a landscape (地形) with enough force to cut deeply into the ground and leaves behind a canyon.可知，这篇文章讲的是峡谷是由洪水下切侵蚀造成的，所以答案是D。