The bottom was clean sand.

水底是干净的沙砾。

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Under UV light, clean sand appears purple or black.

紫外线照射下，干净的沙子呈紫色或黑色。

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First, we put clean sand in a thin glass box, and then we waited for the live ants to arrive.

首先，我们把干净的沙子铺在一个薄薄的玻璃箱子里，然后等待活蚂蚁们到来。

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But the Gold Coast can also surprise even the most dedicated beach snob with its sea hazed dunes, warm waves and soft, clean sand.

BBC: Shore thing: Australia��s beach obsession

Mr Packard's recently signed bill resuscitates the navy's project by allowing the navy to obtain clean sand from anywhere, rather than just from dredging.

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She noticed that if she dipped a sand-covered sweet potato in the water, she could clean it much faster.

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