Do you like traveling? When you visit London, one of the first things you will see is Big Ben, the famous clock which can be heard all over the world on the BBC. If the Houses of Parliament had not been burned down in 1834, the great clock would never have been set up. Big Ben takes its name from Sir Benjamin Hall who made the clock when the new Houses of Parliament were being built. It is not only large, but is very exact（精确的）as well. People have the clock checked twice a day. On the BBC, you can hear the clock when it is actually striking because microphones (麦克风) are connected to the clock tower. Big Ben has rarely gone wrong. Once, however, it failed to give the correct time. A painter who had been working on the tower hung a pot of paint on one of the hands and slowed it down. 

Big Ben is famous all over the world because ____.

A.it is big

B.it is old

C.it tells exact time

D.both A and C