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

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

    The {#blank#}7{#/blank#} (research), led by Professor Rohit Karnik, decided to turn{#blank#}8{#/blank#} 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 {#blank#}9{#/blank#} (amaze), they found that it was effective in trapping all the particles. Greatly {#blank#}10{#/blank#} (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.

    Five months ago. I {#blank#}1{#/blank#}(happen) to be upstairs at dusk when the window was open. I didn't go downstairs until the window had to {#blank#}2{#/blank#}(shut). The dark, rainy evening, the wind and the thundering clouds held me {#blank#}3{#/blank#}(entire) in their power.

    It was the first time in one and a half {#blank#}4{#/blank#}(year) since we found shelter here that I'd seen the night face to face. Sadly I am only able to look at nature through dirty curtains {#blank#}5{#/blank#}(hang) before very dusty windows.{#blank#}6{#/blank#}is no pleasure looking through them because nature is one thing{#blank#}7{#/blank#}really must be experienced. One evening when it was so warm. I stayed {#blank#}8{#/blank#}(wake) on purpose until half past eleven in order to have {#blank#}9{#/blank#}good look at the moon by myself. But as the moon gave far too much light, I {#blank#}10{#/blank#}(not dare) to open the window.

    As an elderly couple was about to shut their phones off onboard a flight to Australia via Abu Dhabi, they noticed a {#blank#}1{#/blank#} (miss) call from their son-in-law. The plane was starting to roll forward on the runway when they {#blank#}2{#/blank#} (see) the text: Their grandson was in special care with {#blank#}3{#/blank#} serious illness. If they didn't get back soon, they might miss their chance to say goodbye.

The couple got the attention of the Etihad Airways crew,{#blank#}4{#/blank#}rushed to tell the pilot. Instead of {#blank#}5{#/blank#} (ignore) their beg to stay on schedule, the kindhearted pilot turned the plane back around to the Manchester Airport gate.

    A hear-warming {#blank#}6{#/blank#} (arrange) was made. From there, the rest of the staff jumped in to get {#blank#}7{#/blank#} (they) home as fast as possible. Some collected their bags and helped the couple through the airport, while others brought their car to arrivals so the grandparents could head straight home. The airline said they could use their tickets another time.

    “I've been in the travel business for {#blank#}8{#/blank#} (decade) and never heard of this happening,” the couple's travel agent, Becky Stephenson, told the BBC. They were aware {#blank#}9{#/blank#} the importance of saying goodbye for the couple, so they offered to help.

    The boy passed away the next day, when his grandparents would have been in Australia, but they reached his bedside in time to say goodbye. The couple felt greatly {#blank#}10{#/blank#}(thank).

    At each stage of our life，we meet different kinds of people. Some are funny； some teach us lessons in life while others occupy a special space in our heart. The people {#blank#}1{#/blank#} (call)"best friends" are just these special friends.

    In our childhood，"best friends" might have meant the persons who are always by our side，{#blank#}2{#/blank#}it may be in the classroom or in the dining hall. However，as we are getting{#blank#}3{#/blank#} (old) than before，our definition(定义)of "best friends" changes. In my opinion，best friends are those who love you {#blank#}4{#/blank#}who you are and help you become who you should be. People in our life come and go，but some people stay. They are the people we should never lose.

    True friends are those who will never leave you when you need them most. They are always there{#blank#}5{#/blank#}(wait)for you and they love you when you forget to love{#blank#}6{#/blank#}(you)．The best feeling in the whole world is knowing that there is {#blank#}7{#/blank#}person who always prays for us and always keeps us in their thoughts. Friendship may not{#blank#}8{#/blank#}(necessary)be based on age，but it is based on{#blank#}9{#/blank#}(understand). Even our parents can be our best friends！So let us build our friendship and try our best {#blank#}10{#/blank#} (see)the good side of everyone!

    In Hebei Province lies a vast forest called Saihanba. This green Great Wall, {#blank#}1{#/blank#} at its peak during the Qing Dynasty covered thousands of hectares, had by the 1950s {#blank#}2{#/blank#}（virtual）disappeared. This allowed sand to blow into Beijing from the northern deserts.

    Saihanba is a combination of Chinese and Mongolian, {#blank#}3{#/blank#}（mean）“beautiful highlands". Until the Qing Dynasty, it was a royal hunting land because of its cool summer weather and beautiful surroundings. However, most of the area had turned into a desert by the end of the Qing Dynasty.

    In fact 56 years ago there was only one tree left. But without that tree, there {#blank#}4{#/blank#}（be）no miracle of Saihanba today. In the early 1960s, over 350 foresters {#blank#}5{#/blank#}（send）to this area to fight the desert. They were required {#blank#}6{#/blank#}（rebuild）the forest in Saihanba. Few people, including the foresters themselves, believed they would succeed.

Their doubt disappeared, however, when they found the 200-year-old tree, swaying alone in {#blank#}7{#/blank#} wind. If one tree could survive here, {#blank#}8{#/blank#} could millions of trees, they thought.

    After decades of hard work, three generations of the foresters have restored almost 80% of the original Saihanba forest. Recently, they were awarded the {#blank#}9{#/blank#}（high）environmental honor from the United Nations for their great {#blank#}10{#/blank#}（contribute）to creating a greener world.