Answer:
A. An unnamed narrator describes Marlow's personality and appearance.
Step-by-step explanation:
This is the main way in which Joseph Conrad uses the frame narrative technique in order to provide characterization of Marlow. A frame narrative is a literary technique that serves as a way to place a story within a story.
Marlow is a recurrent character in several of Conrad's works. He is tough, honest and independent. However, he is also weary, skeptical and cynical. In the book, Conrad presents an unnamed narrator who describes Marlow's personality and appearance.