At the bottom of the hierarchy is a task, the basic element of process activity.

该层次结构的底部是任务，任务是流程活动的基本组成部分。

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Then it discusses the productive nature of tourism from tourism hierarchy, the core position of tourism in leisure activity and tourism supply-demand.

接着，从旅游层次、旅游在休闲活动中的核心地位以及旅游供需的角度具体地分析了旅游的生产本质。

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The third example builds on this last point and suggests a hierarchy of activity stream applications.

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