We promise to keep the sea clean.

我们许诺保持这个海干净。

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The answer is that the seaweeds produce various chemicals that help keep the sea water clean.

答案是海藻产生各种各样的化学物质，这些物质可以保持海水清洁。

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They feed on tiny things in sea water and help to keep the water clean in the process.

它们以海水中的微小物体为食，并在这个过程中帮助保持海水的清洁。

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Others had to keep going and settled on the islands of the Aegean Sea.

其他的则继续逃亡并在爱琴海的岛屿定居

耶鲁公开课 - 古希腊历史简介课程节选

If you keep going east you hit the Black Sea.

如果你一直向东前行就会来到黑海

耶鲁公开课 - 古希腊历史简介课程节选

But there are two big problems with building walls to keep the sea out.

ECONOMIST: Letting the waves rule Britannia

Above all, ASEAN hopes that America will be in a better position to help keep the peace in the South China Sea.

ECONOMIST: South-East Asian summitry

They act as grazers on the ocean floor (manatees are the only other animals that do this), helping keep a balance under the sea for other creatures to live and breed.

FORBES: 12 Days of Charitable Giving 2012: Karen Beasley Sea Turtle Rescue and Rehabilitation Center