"When it comes to Earth，there's no time to waste，"says the Earth Day Network．And that is right．Protecting our environment is very important，and World Earth Day was （16）
in 1970to raise people's environmental awareness．On April 22，People around the world celebrate Earth day．
Every year there is a special （17）
，and this year it is"Trees for Earth"，so Earth Day will be all about planting trees．Their goal is to plant 7.8billion trees （18）
the next five years．
That's a big goal，and you might wonder（19）
trees are so important．Well for one，they can help stop climate change．Carbon dioxide （二氧化碳） is a chemical in our atmosphere，but
（20）
make too much of it．Each person makes about 2.3tons a year，which is bad for the environment．
Well guess what!Trees （21）
carbon dioxide and protect the air quality．Planting new trees is important because people cut down （22）
trees．Last year，there were 3trillion（万亿） trees in the （23）
，about 139billion in China．But according to Time，the world's total number has been （24）
cut in half since human civilization （文明） began．That's because 15billion trees are cut down every year．
So we need to plant more to replenish （补充） the ones e've lost．One tree can take in 48pounds （21.8kg） of carbon dioxide per year．And it's still one of the cheapest and （25）
ways to get rid of carbon dioxide．
But don't forget that you can also help the environment by cutting down on how much energy or water you use every day．Every little thing helps!
| 16．A．set | B．produced | C．created | D．found |
| 17．A．name | B．theme | C．saying | D．sign |
| 18．A．for | B．after | C．by | D．in |
| 19．A．what | B．why | C．whether | D．how |
| 20．A．humans | B．animals | C．ghosts | D．plants |
| 21．A．take out | B．put out | C．take in | D．put in |
| 22．A．countless | B．hopeless | C．useless | D．endless |
| 23．A．wild | B．world | C．forest | D．space |
| 24．A．hardly | B．never | C．really | D．almost |
| 25．A．most | B．best | C．fewest | D．worst． |