Silt and heavy run-off from farms in North Carolina were caused by ______.

A．ordinary people like the television programme
B．ordinary people are interested in pictures of paintings, jewellery, etc.
C．the policemen can not catch the thieves themselves
D．ordinary people may help the policemen get useful information about the criminals

A．helping the police find the criminals and giving the things back to the owners
B．exciting ordinary people
C．making the police popular
D．frightening the thieves