A passage can be identified as a dramatic monologue only when the narrator speaks.
Explanation:
A dramatic monologue is a poem that is written in a dramatic style where the poet creates a character called the persona who narrates the entire poem to a silent and passive listener. Since the narration is just like a monologue in a drama where only the narrator is speaking so this kind of poetry is classified as a Dramatic Monologue.
The Victorian poets greatly specialized in this kind of poetry, Robert Browning being the most popular. His ‘My Last Duchess’ is the most striking example of a dramatic monologue.