题目内容
（请给出正确答案）
[主观题]
一般保温瓶胆为真空玻璃夹层，加层内两侧镀银，能较长时间地保持热水的温度，是因为采取这样的措施，
主要可以减少热水通过瓶胆加层内()方式的热量损失。
A．导热
B．对流换热
C．辐射
D．辐射换热和对流换热
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A. The exchange of an advertisement is triggered by a change in the network.
B. All routers exchange routing tables with each other in a multipoint network.
C. Packets are routed based upon the shortest path to the destination.
D. Paths are chosen depending on the cost efficiency factor.
E. Every router in an OSPF area is capable of representing the entire network topology.
F. Only the designated router in an OSPF area can represent the entire network topology.
