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This is the first, and, thus far, the only, indication of a possible source of exposure.

这是第一次，也是迄今唯一的一次出现可能接触源的迹象。

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Tests taken during an investigation to determine the source of exposure have found a duck positive for H5 in the woman's household.

调查期间为确定接触源开展的检测已发现在该名妇女的家中有一只H5型阳性的鸭子。

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These bills will curb lead levels in water pipes, a major source of harmful lead exposure for children, and help address diesel engine pollution that is linked to serious health conditions like asthma and heart and lung disease.

WHITEHOUSE: Council on Environmental Quality Blog

Certainly, distance from the source and dilution in the atmosphere lowers exposure risk.

FORBES: 1st Person | Facing an Unsettled Future After Radiation Exposure

The WHO said investigations were being conducted into the likely source of the infection, the method of exposure, and the possibility of human-to-human transmission of the virus.

FORBES: Is a New SARS-like Virus Spreading in the Middle East?