手机传递信息的电磁波频率有f₁=900MHz和f₂=1800MHz，与这两个频率相对应的电磁波波长及波速分别是λ₁、v₁和λ₂、v₂，则λ₁ _________λ₂，v₁ ________v₂（以上两空选填“＞”、“=”或“＜”）；除手机外，人们还发明了许多利用电磁波来传递信息的设备，如 ___________（写出一种即可）．

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.

If the jewelry is marked 14 parts of gold mixed with 10 parts of base metal, it will always bear________ mark.

A．a 14K

B．a 10K

C．an 18K

D．a platinum