Final answer:
The author of the book 'William Sydney Porter (O. Henry)' is William Sydney Porter himself, who is known by his pen name O. Henry. He is famous for his short stories with witty narration and twist endings, distinguishing him from other authors like Mark Twain.
Step-by-step explanation:
The author of the book titled William Sydney Porter (O. Henry) is indeed William Sydney Porter himself, who is option 3 among the choices provided. William Sydney Porter is better known by his pen name, O. Henry, and he was a prominent American short story writer. His works are well-known for their wit, wordplay, and twist endings. It's important to distinguish him from other notable authors mentioned such as Mark Twain, Oscar Wilde, and Charles Dickens, each of whom had their own distinct styles and authorship. For instance, Mark Twain, whose real name was Samuel Langhorne Clemens, was an American humorist and author noted for such works as The Adventures of Tom Sawyer and The Adventures of Huckleberry Finn. Twain's works are recognized for their rich storytelling, humor, and critical social commentary. O. Henry's style, while also humorous and engaging, typically resulted in a different form of short story with a surprise ending, setting him apart from Twain's longer and more socially focused narratives.