With a series of strange phenomena_____ , people living in the small village began to suspect that the earthquake was coming.

A to happen   B happening   C happened    D being happened

DiffServ是Internet实现QoS的一种方式，它主要依靠______，其主要缺点是______。

A．不提供全网端到端的Qos保证，可扩展性差
B．中间路由节点需要依据一定的分组标记应用各种PHB
C．只要求在Ds域内Qos的一致性，而在Ds域之间进行相关的映射
D．采用逐跳转发方式，并使用了丢弃策略