Final answer:
Chaucer uses imagery in the General Prologue of The Canterbury Tales to develop the character of the Knight, giving readers visual and concrete descriptions that make him memorable.
Step-by-step explanation:
In Geoffrey Chaucer's The Canterbury Tales, the literary device that Chaucer uses in the General Prologue to flesh out the character of the Knight is d) Imagery. This device is evidenced by the detailed and concrete descriptions Chaucer provides of the Knight's appearance, behavior, and past deeds. The vivid portrayals allow readers to visualize the Knight, making him a memorable and well-defined character in the tales. For example, instead of merely saying the Knight was brave, Chaucer describes him in terms of his participation in various crusades and battles, which brings his character to life more effectively than a simple adjective would.