Final answer:
In "John Henry," a common feature of oral literature is the use of oral-formulaic expression, which is demonstrated through the repetition of certain lines.
Step-by-step explanation:
A common feature of oral literature found in "John Henry" is the use of oral-formulaic expression. Oral-formulaic expression refers to the repetition of phrases or lines that are composed and memorized beforehand, allowing the performer to improvise and vary the delivery while still maintaining the essential structure of the story. In "John Henry," the repeated lines like "Johnny, hold yo' hammer, keep on ringin'" and "John Henry said to his Captain a man," demonstrate this use of formulaic expression.