Routing protocols use different techniques for assigning (81) to individual networks. Further, each routing protocol forms a metric aggregation in a different way. Most routing protocols can use multiple paths if the paths have an equal (82) . Some routing protocols can even use multiple paths when paths have an unequal cost. In either case, load (83) can improve overall allocation of network bandwidth. When multiple paths are used, there are several ways to distribute the packets. The two most common mechanisms are per-packet load balancing and per-destination load balancing. Per-packet load balancing distributes the (84) across the possible routes in a manner proportional to the route metrics. Per-destination load balancing distributes packets across the possible routes based on (85) .

（81）是（）

A.calls

B.metrics

C.links

D.destinations

主动运输不同于自由扩散的特点是（）（1）高浓度-低浓度（2）低浓度-高浓度（3）需要载体蛋白质协助（4）不需要载体蛋白质协助（5）消耗细胞内的能量（6）不消耗细胞内的能量

A．①④⑥

B．②③⑥

C．①④⑤

D．②③⑤