虽不作成分，但也不能省略。

　　5．Encouraging by the speech, the young man made up his mind to take up the struggle.

　　____________________________________________________

　　答案：Encouraging→Encouraged　主语the young man 与

　　encourage之间为被动关系，故应用过去分词作状语。

　　Ⅲ.语法填空

　　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 consisting of scientists from the Massachusetts Institute of Technology (MIT) and high school students__4__were seeking a natural water filter-one that would help communities in developing countries that do not have __5__(accessible) to modern water filter systems.

　　The __6__(research), led by Professor Rohit Karnik, decided to turn to 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 __7__(pour) water containing red dye particles of different sizes through. To their __8__(amaze), 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.

　　1．________2.________3.________4.________5.________ 　6.________7.________ 8.________ 9.________10.________

篇章导读：本文是一篇说明文。树木对人类至关重要，本文通过两个实验证明了树木除了能够提供食物、木材、氧气等作用外，还