问题
选择题
有关物种与生物进化的叙述中，正确的是[ ]
A．物种基因频率的变化意味着新物种的产生
B．野生物种灭绝后会使本物种的基因的多样性降低
C．所有物种的形成都必须经过地理隔离
D．自然选择的实质是选择种群的有利基因，决定了新基因的产生
答案
答案：B
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有关物种与生物进化的叙述中，正确的是[ ]
A．物种基因频率的变化意味着新物种的产生
B．野生物种灭绝后会使本物种的基因的多样性降低
C．所有物种的形成都必须经过地理隔离
D．自然选择的实质是选择种群的有利基因，决定了新基因的产生
答案：B
| The "Karat" marking on jewelry tells you what proportion of gold is mixed with other metals, ff 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. ff 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. |
The Stamping Act is
A．a regulation for tax.
B．role of law.
C．a law that makes such stamping mandate.
D．an implement.