解放军文职招聘考试One possible version

 The boy and the girl in the picture sat on a bench talking merrily while eating a water-melon. When they went away they left the melon’s skin on the bench, making it very dirty. They didn’t want to take any trouble throwing it into the dustbin although it was very near where they were sitting. Instead, they said that there would be someone who should clean the rubbish.

However, what they did violate public morality. If everyone behaves in this way, the world will be a big rubbish dump with flies flying round and people will live in a world of diseases. Besides, dustmen will have a very, very hard job to clean the world we live in.