參考答案： Plant More TreesApril is the best time for green. Everything turns back to life in the warm weather and is enjoying the energy of a new life. Trees are more and more important to the earth. Planting trees is the basic thing to provide a green and healthy environment. Trees, as they are green in color, can make a city or place look more beautiful. It is also valuable in avoiding noises, sandstorms and deserts. It can bring us back a beautiful earth.So, everyone, if you want to make the air clean, please try your best to protect the environment and plant more trees.