Before my work on the writer appeared there were many vague ideas afloat about him.

The word “prevalent” means “widespread or common.” In this context, it would not be accurate to say that there were many prevalent ideas about the writer, because there were many different ideas, and none of them were particularly common.

The word “stagnant” means “not moving or changing.” In this context, it would not be accurate to say that there were many stagnant ideas about the writer, because the ideas were being shared and discussed, which means that they were changing.

The word “primitive” means “of or relating to an early stage of development.” In this context, it would not be accurate to say that there were many primitive ideas about the writer, because the ideas were being shared and discussed, which means that they were not particularly primitive.

In conclusion, the correct answer is A. circulating.