Sand: as children we play on it and as adults we relax on it. It is somethin

游客2024-08-14 13

问题 Sand: as children we play on it and as adults we relax on it. It is something we complain about when it gets in our eye on a windy beach, and praise when it is made into sand castles.
But we don’t often look at it. If we did, we would discover an account of a geological past and a history of sea life that goes back thousands and, in some cases, millions of years.
Sand covers not just seashores, but also ocean beds, deserts and mountains.
【B1】______And it is a major element in manufactured products too—concrete is largely sand, while glass is made of little else.
【B2】______ Well, it is larger than fine dust and smaller than shingle. In fact, according to the most generally accepted scheme of measurement, grains can be called sand if their diameter is greater than 0.06 of a millimetre and less than 0.6 of a millimetre.
Depending on its age and origin, a particular sand can consist of tiny stones or porous grains through which water can pass.
【B3】______They have come from the breaking down of rocks, or from the dead bodies of sea creatures, which collect on the bottom of the oceans, or even from volcanic eruptions.
【B4】______If it is a dazzling white, its grains may come from nearby coral, from crystalline quartz rocks or from gypsum, like the white sand of New Mexico. On Pacific Islands, jet black sands form from volcanic minerals. Other black beaches are magnetic and are mined for iron ore.
【B5】______It washes rock into streams and rivers and down to the sea, leaving behind softer materials. By the time it reaches the sea, the hardest rocks remain but everything else has been broken into tiny particles of 0.02 millimetre diameter or less. The largest pieces fall to the bottom quickly, while smaller particles float and settle only slowly in deeper water, which is why the sandy beach on the shoreline so often turns to mud further out.
Questions 61—65
Complete the passage with the following sentences. There are two extra sentences that you do not need to use.
A. These may have the shape of stars or spirals, their edges rough or smooth.
B. It is one of the most common substances on earth.
C. In addition, it has one vital function which you might never even notice.
D. Rain is an important force in the creation of beaches.
E. In the great slow cycle of the earth, sand that was once rock can turn to rock again.
F. What exactly is sand?
G. Colour is another clue to the origins of sand. [br] 【B4】

选项

答案 G

解析本段介绍的是沙子的颜色。G句可以作为总起句。

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