填空题

Sand covers not just sea-shores, but also ocean beds, deserts and mountains. It is one of the most common substances on earth. And it is a (26) element in man-made materials too— (27) is largely sand, while glass is made by melting sand and some other elements.
What exactly is sand In fact, according to the most generally (28) scheme of measurement, devised by the Massachusetts Institute of Technology, grains qualify as sand if their (29) is greater than 0.06 of a millimeter and less than 0.6 of a millimeter.
Depending on its age and (30) , particular sand can consist of tiny pebbles or porous granules. Its grains may have the shape of (31) or spirals, their edges jagged or smooth. They have come from the (32) of rocks, or from the skeletons of marine organisms, which accumulate on the (33) of the oceans, or even from volcanic eruptions.
Usually, the older the granule, (34) The fine, white beaches of northern Scotland, for instance, are recycled from sandstone several hundred million years old. (35) .
Sand is an irreplaceable industrial factor, which has many uses; but it bas one vital function you might never even notice. Sand cushions our land from the sea’s impact, (36) .