Final answer:
Mark Twain uses direct characterization to depict Adam, explicitly describing his features and thoughts through Adam's own words in a diary format.
Step-by-step explanation:
When Twain characterizes Adam, he mostly uses direct characterization. Mark Twain, known for his wit and satirical style, often employed this literary device to create vivid and memorable characters. Direct characterization happens when the author explicitly describes the personality or physical traits of a character, rather than leaving the reader to infer these traits from the character's actions or dialogue. In his works featuring Adam, such as The Diaries of Adam and Eve, Twain leaves little unsaid about his characters, often using Adam's own words in a diary format to convey his thoughts, feelings, and experiences directly to the reader.