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。

The truth 1.________ trees are vital to our life is not a secret. 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 consisting4.________ scientists from the Massachusetts Institute of Technology (MIT) and high school students 5.________ 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 6.________ (research), led by Professor Rohit Karnik, decided to turn to trees for help 7.________ 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. 8.________ their amazement, they found that it was effective in trapping all the articles. 9.________ (encourage), the team conducted 10.________ experiment, this time with water that contained bacteria. Sure enough, the sapwood held back 99% of the bacteria, allowing only 1% to flow through.