In "Polluted Earth," Cheng uses bold lines to represent the population explosion and the problem of air pollution. The situation is so critical that even the sun is hidden.
在「被汙染的地球」這幅插畫中，鄭明進用簡潔的線條畫出地球上人口爆炸、空氣汙染的危機，人類、動物、植物都紛紛走避，連太陽也都遠遠地躲在一旁，也是一幅頗富教育意義的插畫作品。