（15）Modern cities should be expanding with a certain percentage for green-plant areas.
（16）We must begin now to protect our only earth.
（17）Almost everything we use daily comes from the land directly or indirectly.
（18）But the limited land is decreasing at a surprising speed.
（19）The nature has given us so much, but looks at what we have done in return for its generosity.
（20）The ozone layer is our natural shield in the sky, but this shield is in great danger due to human activities. To protect the ozone layer is to protect us.
（21）Depleting the ozone layer allows more UV-B to reach the earth, which means more skin cancers, more eye cataracts（白内障），weakened immune systems, and reduced plant yield.
（22）The nature has been irritated, which results in the shortage of valuable resources, air pollution, countless acres of lands becoming deserts, etc.
（23）Fortunately, many countries have got to know the seriousness of the problem and take active measures to preserve the environment.
（24）We sincerely hope that all the people in the world will take part in the campaign and join hands to protect the nature.
（25）Besides, trees and lawns in our cities will in the long run help improve the local climate.
（26）The government should also spend more money on the preservation of current lawns and cultivation of new lawns.
（27）Chinese government has taken strict measures to stop careless and indiscriminate felling of trees.
 
（28）Therefore, governments are playing the most important role in environmental protection today.
（29）The government should let people full realize the importance of environmental protection through education.
（30）Cars should be equipped with special devices to reduce auto emission.