根据短文内容，回答下列问题。

    Once there lived a very exactman. One day when he was walking in the street, an old woman came over andasked him, "Excuse me, but where's thenearest restaurant?"

    "The nearest restaurant? Youhave to cross a bridge and then turn to the right," answered the man.

    "Andis the bridge long?"

    "Very,thirty metres."

    The old woman thanked him andwent towards the bridge, Suddenly she heard someone running after her. "Stop!" the man was shouting. "I'mvery sorry. I just remembered the bridge is forty metres long. If you go thirtymetres and then turn to the right, as I told you to do, you will fall into theriver.