Today Newton is avery clean place.Many years ago, however, there were millions of rats in it.Theyattacked the cats and dogs.Sometimes a great number of them knocked
down a man or woman walking home at night.The rats were very large in size andthey harmed many people.
The government ordered everybody to kill rats.Most people were lazy, so theydidn't kill many.The government promised to pay some money for each dead rat.Thatmade
the people very happy.They killed thousands of rats everyday.A governmentofficer put all the dead rats in a big pile.Sometimes a man brought hundreds inone day.
After two weeks there were not many rats in the city, but people still broughtmany rats to the government office.The government officer thought that peoplewere stealing
dad rats from the pile.He ordered his men to dig a deep hole and put the ratsin it.Soon there were no more rats, and the government didn't pay any moremoney.

A deep hole was dugso that ________ .

A.the rats couldn't come out to attack people at night

B.people could take rats from it easily

C.people would kill more rats

D.nobody could take any rats from the pile