Dark matter is a form of stuff that does not interact with light, so cannot be seen, but makes its presence felt by exerting a gravitational pull on normal matter.

暗物质是一种不与光发生作用的物质，因而不可见。但是暗物质又是确实存在的，它与可见物质之间产生的引力效应证实了这一点。

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One can witness a slightly yellower change in the color of the dog's skin, but to the naked eye, fluorescence cannot be seen without the presence of UV light and goggles.

人们可以看到狗的皮肤颜色稍微变黄，但对于肉眼而言，荧光在没有紫外光照射和未使用护目镜时不会被看到。

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But this cannot be seen to happen only on Rwanda's terms.

但这一切却无法得到解决，除非按照卢旺达的条件来办。

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But this cannot be seen to happen only on Rwanda's terms.

ECONOMIST: Violence in Congo

The GOP does not have to take the popular position on every issues, but it cannot be seen as taking radical positions on all ten that are contrary to what so many non hard-core Republican voters believe.

FORBES: Republicans Face A Communication problem with American Voters

One of the oddities of the British debate about the working time directive is that the British could opt out of it for hospitals, and the commission knows that, but cannot say this in public because it cannot be seen encouraging a member government to opt out of an EU directive.

ECONOMIST: European politics