单项选择题
A.How to care for precious metals. B.A standard unit for measuring weight. C.The value of precious metals. D.Using the metric system.
A.Planes and motorcars have taken the place of trains. B.Oil is expensive today. C.Trains are slow. D.Railways lose money.
A.80 dollars. B.60 dollars. C.90 dollars. D.15 dollars.