美国研究者称他们现在知道为什么流感病毒在冬天而不在夏天传播。
American researchers say they now know why the influenza virus spreads in the winter and not in the summer.
美国研究者称，一些世界上重要河流的水位在过去50年里显著下降。
Water levels in some of the world's most important rivers have declined significantly over the past 50 years, US researchers say.
美国研究者称那些游离于星系之外的星球上可能有液态水，因而可能成为传播宇宙生命的跳板。
Liquid water may be found on planets that have gone adrift from their stars and may have acted as stepping stones to spread cosmic life, US researchers say.
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