单选题：根据以下材料回答：Salt,shells or metals are still used as money in ou

根据以下材料回答：Salt,shells or metals are still used as money in out-of-the-way parts of the worldtoday. Salt may seem rather a strange 62 touse as money,63in countries where the food ofthe people is mainly vegetable, it is often an 64necessity.Cakes of salt, stamped to show their 65 , were used as money in some countries until recent66,and cakes of salt 67 buy goods inBorneo and parts of Africa.
Seashells 68 asmoney at some time69another over the greater part of the Old World. These were 70mainlyfrom the beaches of the Maldives Islands in the Indian Ocean, and were traded to India and China. In Africa,shells were traded right across the 71 from East to West.
Metal,valued by weight, 72 coins in many parts of the world. Iron, inlumps, bars or rings, is still used in many countries 73 paper money. It can either be exchanged 74goods, or made into tools, weapons,or ornaments. The early money of China, apart from shells, was ofbronze,75in fiat, round pieces with a hole in the middle, called"cash". The 76of these are between three thousand and fourthousand years old--older than the earliest coins of the eastern Mediterranean.
Nowadays,coins and notes have77nearly all the more picturesque78 ofmoney, and 79in one or two of the more remotecountries people still keep it for future use on ceremonial 80such as weddings and funerals, examplesof81money will soon be found only in museums.
__________ A．object
B．article
C．substance
D．category