Such silica can react when added to cement in the presence of water.

这样的二氧化硅在存在水的情况下加到水泥中时。

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This is true, even in the presence of water treatment systems, they say.

他们说这是真的，甚至在水处理系统中出现。

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This is true even in the presence of water treatment systems , they say .

他们还说现在水资源的处理方法更加使其成为真的。

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So iron left to own devices in the atmosphere in the presence of a little bit of water, with the water form iron oxide.

铁在大气中，在存在,少量水的条件下，大气会开始与水结合产生氧化铁。

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This substance (an iron-magnesium silicate whose greenish colour is reminiscent of olives) weathers rapidly in the presence of water.

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The sample had between 20% to 30% of a type of clay called smectite, which forms in the presence of water, Blake said.

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Spectroscopic images of those rocks taken with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) showed that they were composed of minerals that only form in the presence of water.

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