B应该是in whick contains..错,C,contains和后边may重复,只能又一个谓语动词。错。D, that contain 定语从句修饰Drinking water不可数名词,应该是 that contains. A containing excessive amounts of flourides 修饰drinking water.

tomjinfei (FEI)
(#306887@0)
2001-12-21 -05:00

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