正确答案: C

PaaS

题目：在云计算服务类型中，( )向用户提供虚拟数据的操作系统，数据库管理系统，Web 应用等服务。

解析：C

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举一反三的答案和解析：

[单选题]以下关于关系模式关键字的说法中不正确的是(55)。

一个关系模式只能有一个候选关键字

解析：解析：一个关系模式可以有多个候选关键字，但只能有一个主关键字。

[多选题]●Border Gateway Protocol(BGP) is inter-autonomous system (71) protocol. BGP is based on a routing method called path vector routing. Distance vector routing is not a good candidate for inter-autonomous system routing because there are occasions on which the route with the smallest (72) count is not the preferred route. For example, we may not want a packet through an not secure even though it is the shortest route. Also, distance vector routing is unstable due to the fact that the routers announce only the number of hop counts to the destination without actually defining the path that leads to that (73) ．A router that recevives a distance vector advertisement packet may be fooled if the shortest path is actually calculated through the receiving router itself. Link (74) routing is also not a good candidate for inter-autonomous system routing because an Internet is usually too big for this routing method. To use link state routing for the whole internet would require each routex to have a huge link state database. It would also take a long time for each router to calculate its rousting (75) using the Dijkstra algorism.（71）

routing

switching

transmitting

receiving

path

hop `

route

packet

connection

window

source

destination

status

search

state

research

table

state

metric

cost

解析：A,B,D,C,A