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 _____.