Nowadays， there are more and more in . It is estimated that ___. Why have there been so many ____? Maybe the reasons can be listed as follows.
The first one is ______. Besides，_____. The third one is _____. To sum up， the main cause of it is due to _____. It is high time that something were done upon it. For one thing，_____. For another thing， _____. All these measures will certainly reduce the number of _____.