Trees around us are extremely important and have always been necessary for improving the human conditions. Our existing forests and trees we plant work to make a better world.    1    . Here is a short list of main reasons trees are necessary for improving our living conditions.

Trees produce oxygen    2    . A leafy tree produces as much oxygen in a season as 10 people inhale in a year. What many people don't realize is that the forest also acts as a giant filter (过滤器) that cleans the air we breathe. Trees help clean the air by preventing airborne particles, reducing heat, and absorbing such pollutants. Trees clean the soil. The term phytoremediation is a fancy word for the absorption of dangerous chemicals and other pollutants that have entered the soil.

    3    . Trees filter sewage and farm chemicals, reduce the effects of animal wastes, clean roadside spills and so on. Trees are carbon sinks. To produce its food, a tree absorbs and locks away carbon dioxide in the wood, roots and leaves.

Carbon dioxide is a global warming suspect.    4    . This locking­up process “stores” carbon as wood and not as a “greenhouse” gas.

    5    Trees block urban noise almost as effectively as stone walls. Trees, planted at strategic points in a neighborhood or around your house, can reduce major noises from freeways and airports.

3 . I fell in love with Yosemite National Park the first time I saw it, when I was 13. My parents took us there for camping. On the way out, I asked them to wait while I ran up to E1 Capitan, a _______ rock of 3,300 feet straight up. I touched that giant rock and knew _______ I wanted to climb it. That has been my life’s passion (钟爱) ever since— _______ the rocks and mountains of Yosemite. I’ve long made Yosemite my _______.

About 15 years ago I started seeing a lot of _______, like toilet paper, beer cans, and empty boxes, around the area. It’s _______ me why visitors started respecting the place _______ and treated such a beautiful home-like place this way.

I tried _______ trash (垃圾) myself, but the job was too big. I would _______an hour or two on the job, only to find the area trashed all over again weeks later. Finally, I got so _______ it that I decided something had to change.

As a rock-climbing guide, I knew ________about organizing any big event. But in 2004, together with some climbers, I set a date for a ________. On that day, more than 300 people ________. Over three days we collected about 6,000 pounds of trash. It was amazing how much we were able to ________. I couldn’t believe the ________ we made—the park looked clean!

Each year volunteers come for the cleanup from everywhere. In 2007 alone, 2,945 people picked up 42,330 pounds of trash and ________ 132 miles of roadway.

I often hear people ________ about their surroundings. If you are one of them, I would say the only way to change things is by ________ rather than complaining. We need to teach by ________. You can’t blame others ________ you start with yourself.