Final answer:
Winston initially sees O'Brien as a sophisticated and potentially charming Inner Party member who seems to be a firm believer in the Party's ideology, yet he senses a complex undercurrent in his persona.
Step-by-step explanation:
Winston's initial impression of O'Brien is best described as B: a charming man who may completely believe in the party's orthodoxy. O'Brien appears to be a member of the elite Inner Party, knowledgeable and sophisticated, which strikes Winston as someone who is deeply loyal to the Party's cause. However, this initial impression is layered with a sense of intrigue, as Winston also perceives a certain complexity in O'Brien that suggests he might harbor unorthodox thoughts similar to Winston's own.