問題詳情

(F)The earth has always been home to the human race. But how much do we really know about this planet? The Earth is constantly altering. Some of the changes are obvious -- day turns to night, spring turns to summer. These changes are caused by the Earth’s rotation on its axis and by its orbit around the sun. But deep inside the Earth, heat within the mantle is also causing structural effects on the outer skin, or crust, of the Earth. In addition to the natural changes on Earth, there are those caused by the human race. Activities such as farming, mining and the building of towns and cities alter the face of the Earth. Pollution poisons the rivers, lakes and air -- even the protective screen of the atmosphere has been affected by the release of chemicals into the air. The overall result is that much of the Earth’s well-balanced ecological system is being destroyed. A better understanding of our planet -its rocks, soil, water and gases -- will help us preserve the Earth for the future.The Earth was formed about 4,500 million years ago. It is not a true sphere but slightly flattened at the poles. The deepest hole ever drilled into the crust of the Earth reached a depth of 15 km (less than 10 miles). This is the merest pinprick on the surface of the whole vast globe, 12,750 km (7,900 miles) in diameter, on which we live. We have direct experience only of the rocks in the crust, the water in the oceans and the gases in the atmosphere that surrounds the Earth. What scientists know about the interior comes from indirect evidence, such as the patterns of earthquake waves as they pass through the Earth. They can also analyze the composition of meteorites, and make certain deductions about the substances that lie inside the earth deep beneath our feet, assuming that the meteorites have the same origin as the earth and everything else in the Solar System.A world map shows the linked continents of the Americas, the continuous sweep of Europe, Asia and Africa, isolated Australia, and desolate Antarctica sitting over the South Pole. Yet it was not always like this. Throughout time the continents, and indeed the entire Earth’s surface, have been constantly in motion. The process is known as plate tectonics. It has been understood only since the middle of the 20th century, because most of the effects can be seen only at the ocean bottom. But knowledge of plate tectonics is fundamental to an understanding of the processes that shape the Earth.
72. Which of the follo
(A) Taking turns or recurring in a particular order.
(B) Moving in circles round a central point.
(C) Making something move faster or happen
(D) Traveling at top speed.

參考答案

答案：B
難度：適中0.5
統計：A(0),B(0),C(0),D(0),E(0)

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