但是，气候条件存在波动，造成干湿天气交替，以致可以获取的动植物数量忽高忽低。

There were, however, fluctuations in the climatic conditions, with the consequences that wet conditions were followed by dry ones, so that the availability of plants and animals oscillated brusquely.

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如果条件存在，核爆产生的放射性尘降物会随风漂移数百英里。

Fallout from a nuclear explosion may be carried by wind currents for hundreds of miles if the right conditions exist.

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如果条件存在，条件的值必须为true才能将该值作为结果返回。

If a condition exists, the condition must evaluate to true in order for the value to be returned as the result.

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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。

麻省理工公开课 - 热力学与动力学课程节选

But the presence of the dog there is a conditioned stimulus and so you grew to be afraid of dogs.

而这时狗的存在就变成了条件刺激,所以你开始对狗心生恐惧。

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One of the things that estrogen does when cells are exposed to estrogen is that certain genes get turned on that weren't turned on in the estrogen-free state.

雌激素的功能是,当细胞所处环境中有雌激素时,一些在雌激素不存在的条件下,无法表达基因就能够表达

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