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找不到好的英语六级听力练习材料?绝对是你的不二选择。大家平时多用英语磨耳朵，时间长了英语六级听力绝对会有很大的提高。 英语六级听力练习：标准4.9 点击收听 Scientists have discovered the worlds earliest known cardiovascular system - heart and blood vessels - in the fossil of a shrimp-like creature from more than 500 million years ago. The rare find sheds new light on the evolutionary timeline of life on Earth. The Yunnan Province in southwestern China is known for rich fossil deposits, but researchers had not expected a fossil so exquisitely preserved as the specimen of the 520-million-year-old shrimp-like species. Researcher Peiyun Cong with the Yunnan Laboratory for Paleobiology unearthed the fossil, which gave researchers the first detailed image of the creatures circulatory system. [The fossil] is a beautiful carbon trace, said University of Arizona neuroscientist and team member Nicholas Strausfeld. It is bilaterally symmetrical. It shows the dorsal blood vessel and the lateral vascular components, the arteries, the lateral arteries and then a very, very, beautiful, system of arteries over where the brain sits in the head. In earlier research with fossils of the same species, the scientists on this project had identified its brain, gut and nervous system. | 
