题目内容：

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。

It is not a secret 1.    trees are vital to our life. They provide us with food, wood and most 2.    (important), oxygen. Now there is one more thing we can add to this list—blocking out harmful bacteria from water.

The discovery 3.     (make) by a team 4.    (consist) of scientists from the Massachusetts Institute of Technology (MIT) and high school students 5.   were seeking a natural water filter(过滤)—one that would help communities in developing countries that do not have 6.    (accessible) to modern water filter systems.

The 7.    (research), led by Professor Rohit Karnik, decided to turn8.______ trees for help, because 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. To their 9.    (amaze), they found that it was effective in trapping all the particles. Greatly 10.   (encourage), the team conducted another experiment, this time with water that contained bacteria. Sure enough, the sapwood held back 99% of the bacteria, allowing only 1% to flow through.