Complete the following passage with the words in the box. Each can only be used once（将下列单词填入空格。每空格限填一词，每词只能填一次）| A. enough B. serious C. resource D. centuries E. precious |
From deserts to beaches to playgrounds, sand is found almost everywhere. It is a common sight. But you might not know that it is very 16 .
Sand is widely used in glass-making and road-building. It is the second most-used 17 after water in the world, the BBC reported. However, the UN said that sand is not limitless and that we might be running out of it.
Sand is made up of very small pieces of rock, soil and minerals. It can take thousands of 18 to form, but now we are using sand too quickly. According to the BBC, we use about fifteen billion tons of sand every year to build houses, roads etc. That is 19 to build a 20-meter-high by 20-meter-wide wall around the equator（赤道）every year. Can you believe it?
| A. disappear B. probably C. continue D. sometimes E. seldom |
People 20 put sand into the sea to make new islands. Singapore, for example, is now 20 percent bigger than it was in 1965. Palm islands are three large man-made islands in Dubai, United Arab Emirates. They took 94 million cubic meters of sand to build.
If people 21 using this much sand, it will run out in many places. For example, Vietnam may run out of construction sand by 2020, Live Science noted.
Since people need so much sand, they are trying to mine（开采）more of it. But this is bad for the environment. Mining sand may cause beaches to 22 and more floods to happen in places close to the sea. Also, this will 23 affect the habitats（栖息地）of many plants and animals.
