阅读下面材料，在空白处填入适当的内容(1个单词)或括号内单词的正确形式。
The truth ____ trees are vital to our life is not a secret. They provide us withfood, wood and most ____(important), oxygen. Now there is one more thing we canadd to this list—blocking out harmful bacteria from water.
The discovery ____(make) by a team____(consist) of scientists from the Massachusetts Institute of Technology(MIT) and high school students ____ were seeking a natural water filter—onethat would help communities in developing countries that do not have ____(accessible)to modern water filter systems.
The ____(research), led by Professor RohitKarnik, decided to turn to trees for help because they could allow liquid toflow through, while blocking out air bubbles.
They began by cutting 1.5inchwide sectionsof tree bark from the branches of a white pine tree. The people related thentested the wood's filtering ability by pouring water containing red dyeparticles of different sizes through. ____ their amazement, they found that itwas effective in trapping all the particles. ____(encourage), the teamconducted ____ experiment, this time with water that contained bacteria. Sureenough, the sapwood held back 99% of the bacteria, allowing only 1% to flowthrough.
