A sheet of metal can be shaken to ________ thunder.

A．it is vital for us to be truthful to each other
B．lying will be checked by more advanced lie detectors
C．a lie detector can make a good record of nerve impulses
D．a liar benefits himself from lying, but only at the cost of others

A．we are convinced that men are born evil
B．human beings are surrounded by piles of rubbish
C．there are a lot of obstacles on the way ahead of human beings
D．man's future is seen to be better advantage from his good nature