Ferrous metals include iron and alloys ofat least 50% iron.

A、great heat resistance

B、great impact resistance

C、low density

D、great strength

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 【B1】 to use as money, 【B2】 in countries where the food of the people is mainly vegetable, it is often an 【B3】 necessity. Cakes of salt, stamped to show their 【B4】 , were used as money in some countries until recent 【B5】 and cakes of salt 【B6】 buy goods in Borneo and parts of Africa. Sea shells 【B7】 as money at some time 【B8】 another over the greater part of the Old World. These were 【B9】 mainly from 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 【B10】 from East to West. Metal, valued by weight, 【B11】 coins in many parts of the world. Iron, in lumps, bars or rings, is still used in many countries 【B12】 paper money. It can either be exchanged 【B13】 goods, or made into tools, weapons, or ornaments. The early money of China, apart from shells, was of bronze, 【B14】 in flat, round pieces with a bole in the middle, called "cash". The 【B15】 of these are between three thousand and four thousand years old--older than the earliest coins of the easterr Mediterranean. Nowadays, coins and notes have 【B16】 nearly all the more picturesque 【B17】 of money, and 【B18】 in one or two of the more remote countries people still keep it for future use on ceremonial 【B19】 such as weddings and funerals, examples of 【B20】 money will soon be found only in museums.

【B1】

A．object

B．article

C．substance

D．category

A、need

B、are needing

C、are needed

D、will need