Thetruth 46 treesarevitaltoourlifeisnotasecret.Th...

问题详情：

       The truth  46  trees are vital to our life is not a secret. They provide us with food, wood and most 47  (important), oxygen. Now there is one more thing we can add to this list—blocking out harmful bacteria from water.111]

    The discovery 48  (make) by a team consisting 49  scientists from the Massachusetts Institute of Technology (MIT) and high school students 50  were seeking a natural water filter—one that would help communities in developing countries that do not have access to modern water filter systems.

    The 51  (research), led by Professor Rohit Karnik, decided to turn to trees for help 52  they could allow liquid to flow through, while blocking out air bubbles.

    They began by cutting 1.5-inch-wide sections of tree bark from the branches of a white pine tree. The people related then tested the wood’s filtering ability by pouring water containing red dye particles of different sizes through. 53  their amazement, they found that it was effective in trapping all the articles. 54  (encourage), the team conducted 55 experiment, this time with water that contained bacteria. Sure enough, the sapwood held back 99% of the bacteria, allowing only 1% to flow through.

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