在物质流动动力学模型(dynamic model)中曾假设产品寿命（ ） What is assumed for the product life span in the material flow dynamics model is （ ）

A、约等于其它过程所花费的时间 The product life span is approximately equal to the time taken by other processes
B、远大于其它过程所花费的时间 The product life span is much longer than the time taken by other processes
C、远小于其它过程所花费的时间 The product life span is much less than the time taken by other processes
D、与其它过程所花费的时间无关 The product life span is independent of the time spent in other processes