反复比较各个在线商场的商品，对所要购买的商品的特点、性能和使用方法心中有数后产生购买动机，这种动机是一种（）？

A.理智动机

B.感情动机

C.惠顾动机

D.虚拟动机

In software engineering and systems engineering, (71) is a description of a system's behavior as it responds to a request that originates from outside of that system．

A．black box
B．business rule
C．use case
D．traceability matrix