阅读理解
The "Karat" marking on jewelry tells you what proportion of gold is mixed with other metals. If 14 parts of gold are mixed with 10 parts of base metal, the combination is called 14-Karat (14K) gold. The higher the Karat rating, the higher the proportion of gold in the object. The lowest Karat gold that can be marketed in the United States is 10-Karat gold. Jewelry does not have to be marked with its Karat quality, but most of it is. If there is a Karat quality mark, next to it must be the U.S. registered trademark of the person or company that will stand behind the mark, as required by the National Gold and Silver Stamping Act.
单选题
If a ring is stamped 24K, it has________.
【正确答案】
B
【答案解析】推断题型。见文中第二句：If 14 parts of gold are mixed with 10 parts of base metal，the combination is called 14-Karat(14K)gold．如果将14份黄金与10份普通金属混合，它们的化合物即14K金。由此可推论24K金应为24份黄金与10份普通金属混合。所以选项B．“如果一只戒指上刻24K，它应含有24份黄金。”是答案。
单选题
Gold which is 10 Karats in proportion ________in the U.S.
【正确答案】
D
【答案解析】细节题型。见文中：The lowest Karat gold that can be marketed in the United States is 10-Karat gold．能够在美国市场上交易的黄金最低含金量不能低于10K。因此选项D．“10K的黄金是美国能够上市的最低级别的黄金。”是答案。
单选题
If gold is marked with a Karat quality mark, it must also bear________.
【正确答案】
B
【答案解析】细节题型。见文中：If there is a Karat quality mark，next to it must be the U.S. registered trademark of the person or company that will stand behind the mark…．如果黄金饰品上标有开／K纯度的质量标志，紧挨这个标志的后面一定要有某个在美国注册的个人或公司的商标。选项B与此同义，故为答案。
单选题
If the jewelry is marked 14 parts of gold mixed with 10 parts of base metal, it will always bear________ mark.
【正确答案】
A
【答案解析】细节题型。
单选题
This paragraph serves the consumer as________.