Final answer:
The stream-of-consciousness technique is the aspect of Faulkner's storytelling in "As I Lay Dying" that makes it a modernist piece of literature.
Step-by-step explanation:
The aspect of Faulkner's storytelling in "As I Lay Dying" that most makes it a modernist piece of literature is the stream-of-consciousness technique. This technique is characterized by a narrative style that mimics the thought processes and inner experiences of the characters, often without a linear structure. Faulkner employs this technique extensively in the novel, using fifteen different characters to provide their fragmented and subjective perspectives on the death and burial of the matriarch.
This stream-of-consciousness technique reflects the modernist interest in exploring the human psyche and the complexities of individual experience.