article: Today Newtown is a clean place, but many years ago there were millions of rats there. The rats even attacked ( ) the cats and dogs. Sometimes many of them tried to bite men or women at night. The rats were very large in size and they harmed ( ) many people.
  The city office ordered every one to kill rats. However, most people were lazy, so they did not kill many rats. The city office could do nothing with the citizens and could do nothing with the rats, either. Some time later, they had to pay some money for each dead rat. That made the people very happy. They at once began to kill rats. They got as many dead rats as they could. And some of them even stopped their own work to kill rats because they could get more pay. Every day a city official( ) put all the dead rats together. He was very busy doing that, because sometimes a man brought hundreds of them in one day. Two weeks later, there were not so many rats in the city as before,  but people still brought many dead rats to the city office. The city officials felt surprised at this but at last they found out people were stealing the dead rats they had collected. So the city official had to order his men to dig a big hole and put the dead rats in it. Soon there were no more rats and the city did not have to pay any more money for that.
question: A big hole was dug so that   _  .
options: the rats could come out to attack people at night people could take many rats the people loved dead rats people could not steal dead rats for money