Which of the following statements regarding Stone-Copper Age are true?; I. Stone-Copper culture had an essentially urban background.; II. Inspite of food producing economy, the rate of infant morality was very high.; III. People were not aware of the art of mixing tin with copper and thus forging the much stronger and useful metal called bronze.; IV. People of this age were familiar with the art of writing and they used to live in the cities as people of bronze age.