在利用现有直流电动机设计过程中，考虑到晶闸管变流器供电方式交流侧谐波等问题，建设单位要求设计

总需求的外部性(aggregate-demand externality)

外部性(externality)

试以举例的方式，借助几何图形简要分析网络外部性(network externality)之正外部性——攀比效应(bandwagon effect)。

试以举例的方式，借助几何图形简要分析网络外部性(network externality)之正外部性——攀比效应(bandwagon effect)。

A．positive externality, as does the use of a common resource

B．positive externality and the use of a common resource generates a negative externality

C．negative externality, as does the use of a common resource

D．negative externality and the use of a common resource generates a positive externality