These are rings of 18 and 24 karat gold.这些是18K和24K金的.This necklace of mine is not very expensive, it is 18 - karat gold.我这个项链不太贵, 是18开金的.Gold jewelry of 10 K or more will have a karat stamp.含金量为10K或者高于10K的黄金饰品上将会有K金标志....
化石燃料（如煤和石油）属于有限资源。The fossil fuels (coal and oil) are finite resources.用煤作燃料的火力发电站的成本有望降低。The cost of electricity from coal-fired stations is expected to fall.当局已经敦促人们储备燃料。The authorities have urged people to stock up on...