题目内容：
根据下列文字，回答题。Decide which of the choices given below would best complete the passage if inserted in the corresponding blanks. Mark the best choice for each blank on your answer sheet.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 (31)__ to use as money, (32)__ in countries where the food of thepeopleismainlyvegetable,itisoftenan (33)__________necessity. Cakes of salt, stamped to show their (34) __________, were used as money in some countries until recent (35) and cakes of salt (36) __________ buy goods in Borneo and parts of Africa.
Sea shells (37) __ as money at some time (38) __________ another over the greater part of the Old World.These were (39) __ mainly from the beaches of the Maldives Islands in the Indian Ocean, and were traded to India and China. In Africa, shells were traded fight across the (40) __________ from East to West.
Metal, valued by weight, (41) __________ coins in many parts of the world. Iron, in lumps, bars or rings, is still used in many countries (42) __________ paper money. It can either be exchanged (43) __________ goods, or made into tools, weapons, or ornaments. The early money of China, apart from shells, was of bronze, (44) __________ in flat, round pieces with a hole in the middle, called "cash". The (45) __ 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 (46)__ nearly all the more picturesque (47)__ of money, and (48) __________ in one or two of the more remote countriespeoplestillkeepitforfutureuseon ceremonial (49)__________ such as weddings and funerals, examples of(50)__ money will soon be found only in museums.回答第31空。 A．object
B．article
C．substance
D．category
参考答案：
答案解析：