只写5个空即可，最后一个空和第一个空的词一样，不用单写出来。
Life on Earth requires six basic ingredients—carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus. Those six elements are the ____1____ for DNA and RNA, along with proteins and fats. Which means they're essential for life—as we know it. But it might be time to update that list. Because scientists have found a bacterium that can do without phosphorus—live on arsenic instead.
The researchers had a ____2____ a bug like this might exist, because arsenic has some ____3____ in common with phosphorus. So they collected mud from California's Mono Lake, where the waters are naturally salty, and laced with arsenic. Back in the lab, they cultured microbes from that mud. But instead of adding phosphorus to the cultures to help the bugs grow, they added varying levels of arsenic.
One bacterial ____4____ continued to thrive. And tests confirmed that the organisms ____5____ the lack of phosphorus by building their DNA with arsenic instead. The research appears in the journal Science.
This is the first known life form that seems to be able to swap out one of life's fundamental ____1____ with another element. So for astrobiologists hunting for life in space, don’t rule out places filled with poison.
【视听版科学小组荣誉出品】
building blocks hunch chemical properties strain compensated for
地球上的生命体需要六种基本元素——碳、氢、氮、氧、硫和磷。这六种元素以及脂肪和蛋白质是DNA和RNA的构成要素，也就是说，和我们知道的一样，它们是生命体所必须的。但也许是时候更新这份必需元素目录了，因为科学家们发现一种细菌会用砷来代替磷，不需要磷也可生存。因为砷和磷有一些相同的化学特性，研究人员早有预感有这种细菌存在。因此他们从加利福尼亚的莫诺湖收集了一些泥土。莫诺湖水天然带咸并含砷。回到实验室后，研究人员开始培养泥土中的微生物。但是他们加进去帮助微生物生长的元素并不是磷，而是不同分量的砷。 一种细菌在这种情况下继续繁殖，而检测证实这种生命用砷代替了缺乏的磷合成了它们的DNA。这项发现刊登在《自然》杂志上。这是人们发现的第一种可以用其他元素取代生命基本构成要素的生物。因此那些在太空寻找生命的天体生物学家们，可不要忽略了那些充满毒药的地方哦！:P