The answer is letter A. You're generating words that suggest possible sentences or paragraphs.
It is not chronological or suggests possible themes. Clustering only happens when there is a theme already. When in clustering, thoughts are tumbled out, enlarging vocabulary word bank and enabling to see patterns of ideas. It may be done individually or by class.
Clustering is akin to brainstorming. It is an activity wherein ideas, images, and feelings are generated around a stimulus.