There are many ways to save the environment if you would like. In this passage, you can find some ways.
$Plant more trees. Choose a right (^1)$$ near your house or workplace. (^2)$$ there's any rule stopping you from growing trees in that area, go ahead and grow trees. Plant a tree every month and (^3)$$ your friends and classmates to join you. Have more and more trees (^4)$ and there will come a day when you have green land thanks to your hard work.
$Walk more and drive less. Choose to walk (^5)$$ than drive your car. Walk or ride a bicycle to work if it's not very far. Not only cycling but walking is good exercise. And each time you avoid using your car, you're doing something (^6)$ to cut down air pollution. You are saving fuel, saving money and keeping fit as well.
$Save water. Water is very important for living things. It's we who use and (^7)$$ it. The simplest way to save water is turning (^8)$$ water taps after use. When you visit a beach, make sure that you don't litter around. Do not pollute rivers (^9)$$ dropping garbage or other waste. Water is precious, so we (^1⁰)$ waste or pollute it.

1. ground  
2. Unless
3. encourage
4. planted
5. rather
6. helpful
7. pollute
8. off
9. by
10. can't

1. 第一个空需要一个名词，根据上下文，这里指的是选择一个合适的“地方”来种树，因此填“ground”。
2. 第二个空需要一个连词，引导条件状语从句，表示“除非”有规定阻止，否则就可以种树，因此填“Unless”。
3. 第三个空需要一个动词，根据句意是鼓励朋友和同学加入种树的活动，因此填“encourage”。
4. 第四个空需要一个动词的过去分词形式，构成“have sth. done”结构，表示让树被种植，因此填“planted”。
5. 第五个空需要一个副词短语，与“drive”形成对比，表示选择走路而不是开车，因此填“rather”。
6. 第六个空需要一个形容词，描述避免使用汽车对减少空气污染是有益的，因此填“helpful”。
7. 第七个空需要一个动词，与“use”并列，表示我们使用并且污染水，因此填“pollute”。
8. 第八个空需要一个副词，描述关掉水龙头的动作，因此填“off”。
9. 第九个空需要一个介词，表示通过丢弃垃圾来污染河流的方式，因此填“by”。
10. 第十个空需要一个情态动词，表示我们不能浪费或污染水，因此填“can't”。