战略群组分析有助于企业了解相对于其他企业本企业的战略地位以及公司战略变化可能的竞争性影响。具体来讲，其意义有()。

A.有助于很好地了解战略群组间的竞争状况 

B.有助于了解各战略群组之间的“移动障碍” 

C.有助于了解战略群组内企业竞争的主要着眼点 

D.可以预测市场变化或发现战略机会

In low-speed network, it is usually adequate to wait for congestion to occur and then react to it by telling the source of packets to slow down. In high-speed networks, this approach often works poorly, because in the ______ between sending the notification and notification arriving at the source, thousands of additional ______ may arrive. In ATM network, a major tool for preventing ______ is ______ control. When a host wants a new virtual ______, it must describe the traffic to be offered and the service expected.

A．packets
B．cells
C．message
D．files