北下列关于地球上存在生命的条件说法错误的是

A．位于安全稳定的宇宙环境

B．有生物圈存在

C．日地距离适中

D．体积质量适中

In the Ethernet LAN, an algorithm was chosen to dynarnically adapt to the number of stations trying to send. It is called

A． backward learning

B． binary exponential backoff

C． spanning tree

D． CRC