问题
单项选择题
The network layer provides services to the ______ layer. It can be based on either virtual circuits or datagrams. In both cases, its main job is routing packets from the source to the destination.
A．transport
B．application
C．presentation
D．data link
答案
参考答案：A
解析：[参考译文] 网络层为传输(transport)层提供服务，它基于虚电路或数据报方式，其主要工作是对源节点的数据包进行路由选择，转发到目的节点。