Step 1: Understanding the Concept:
This question asks to identify the author of a famous line from American poetry.
Step 2: Detailed Explanation:
The line, "I celebrate myself, and sing myself, / And what I assume you shall assume, / For every atom belonging to me as good belongs to you," is from the opening section of Walt Whitman's epic poem, "Song of Myself". This line establishes the poem's central theme of democratic universalism: the idea that the self (the "I" of the poet) is fundamentally connected to all other selves (the "you" of the reader) and to all of nature at a basic, atomic level.
Step 3: Final Answer:
The author of this line is Walt Whitman. Therefore, option (B) is the correct answer.