中国大学MOOC: Needs of different levels should be met one by one and level by level.

Fiction has two levels of understanding, the narrative level and the<br/>authorial level, or the <br/>surface<br/>level and the deep level of understanding.()

中国大学MOOC: The design feature of __________ refers to the property of having two levels of structures, such that units of the primary level are composed of elements of the secondary level.

The culture shown in an onion consists of two levels; a level of norms and values, or an invisible level of resultant behavior or artifacts of some form.

中国大学MOOC: _________ is one of the design features of human language which refers to the phenomenon that language consists of two levels: a lower level of meaningless individual sounds and a higher level of meaningful units.