【单选题】

Salt, shells or metals are still used as money in out-of-the-way parts of the world today.

Salt may seem rather a strange (1) to use as money, (2) in countries where the food of the people is mainly vegetable, it is often an (3) necessity.Cakes of salt, stamped to show their (4) , were used as money in some countries until recent (5) , and cakes of salt (6) buy goods inBorneo andDarts ofAfricA、
Sea shells (7) as money at some time (8) another over the greater part of the Old WorlD、These were (9) mainly from the beaches of the Maldives Islands in the Indian Ocean, and were traded to India andChinA、InAfrica, shells were traded fight across the (10) fromEast to West.
Metal, valued by weight, (11) coins in many parts of the worlD、Iron, in lumps, bars or rings, is still used in many countries (12) paper money. It can either be exchanged (13) goods, or made into tools, weapons, or ornaments. The early money ofChina, apart from shells, was of bronze, (14) in flat, round pieces with a hole in the middle, called "cash". The (15) of these are between three thousand and four thousand years old-older than the earliest coins of the eastern Mediterranean.
Nowadays, coins and notes have (16) nearly all the more picturesque (17) of money, and (18) in one or two of the more remote countries people still keep it for future use on ceremonial (19) such as weddings and funerals, examples of (20) money will soon be found only in museums.
A．while
B．although
C．because
D．if