An active continental margin has while a passive margin does not

The given blank can be filled with subduction.

Explanation:

An active continental margin is witnessed on the prominent edge of the continent where it is colliding into an oceanic plate, that is, the process of subduction taking place. The active margins are generally the locations of tectonic activity.  

On the other hand, passive continental margins are witnessed along the left coastlines. As there is no subduction or collision occurs, there is least tectonic activity taking place and the processes of erosion and weathering take place the most.  

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