Coasts mark the area where dry land meets oceans or other large bodies of water. They are one of the most active environments fo

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问题     Coasts mark the area where dry land meets oceans or other large bodies of water. They are one of the most active environments found on Earth. The coastal landscape is ever-changing. It reflects the conflicting processes of erosion and deposition. It is a landscape that is affected by the interactions of the Earth, the Moon, and the Sun.
    Coasts are among the most beautiful and inspiring landscapes on the planet, whether they are scenes of torrential storms or serene calm. Throughout recorded history, humans have sought to live on or near coasts. Although coasts account for only 10 percent of Earth’s land surface, they serve as home to two thirds of the world’ s human population.
    Coasts and shore, coastline and shoreline, are commonly used in place of each other. Technically, they are different areas along a coastal landscape. The line that marks the boundary between water and land is the shoreline. It constantly fluctuates because of the regular action of waves and tides. The shore is that strip of ground bordering a body of water that is alternately covered or exposed by waves or tides. The boundaries of the shore are marked by the shoreline at its farthest seaward(low tide)and farthest landward(high tide).
    Tide is the periodic rising and falling of water in oceans and other large bodies of water in response to the gravitational attraction of the Moon and the Sun upon Earth. Although the Sun is larger than the Moon, the Moon is closer to Earth and, therefore, its gravitational force is approximately 2.2 times greater. The gravitational pull of the Moon creates two types of tides: high and low. A tidal bulge occurs in the oceans on the side of Earth nearest the Moon, at the same time, a second tidal bulge occurs on the opposite side of Earth. This second bulge forms because the force of the Moon’s gravity pulls the solid body of Earth slightly away from the water on Earth’s far side. These bugles are high tides. The areas between the tidal bulges experience low tide.
    As Earth rotates, the tides move over its surface. It takes approximately 24 hours and 50 minutes for a given point on Earth to make a complete cycle relative to the Moon, and two lunar tidal cycles occur during this time. Thus, the average time between high tides is 12 hours and 25 minutes. This is a generalized explanation of tides. They do not move evenly and predictably over Earth’s surface. Variations in the depth of the oceans and the distribution of landmasses combine with other factors to produce highly complex tidal behavior.
    The coast and coastline begin where the shore ends at its high tide mark(farthest landward). The line between the coast and the shore at high tide is the coastline. The coast extends landward from the coastline to the first major change in terrain features, which may be miles inland. This could be a highland or a forest or some other type of terrain. Sometimes, the change between the coast and the adjacent terrain is not so distinct.
One lunar tidal cycle lasts______.

选项 A、24 hours and 50 minutes
B、12 hours and 25 minutes
C、a month
D、half a month

答案B

解析 根据文章第五段的第二句“It takes approximately 24 hours and 50 minutes…and two lunartidal cycles occur during this time.”判断可知,一次月潮持续12小时25分钟。
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