A、Something made of either metal or paper. B、Pieces of metal. C、Printed notepaper. D、Something useful for starving travelers. A

Aristotle, the Greek philosopher, summed up the four chief qualities of money some 2,000 years ago. It must be lasting and easy to recognize, to divide, and to carry about. In other words it must be, durable, distinct, divisible and portable. When we think of money today, we picture it either as round, flat pieces of metal which we call coins, or as printed paper notes. But there are still parts of the world today where coins and notes are of no use. They will buy nothing, and a traveler might starve if he had none of the particular local money to exchange for food.
    Salt may seem rather a strange substance to use as money, but in countries where the food of the people is mainly vegetable, it is often an absolute necessity. Cakes of salt, stamped to show their value, were used as money in Tibet until recent times, and cakes of salt will still be used to buy goods in Borneo and parts of Africa.