Because Irish Immigrants, Native Americans, and African Americans were all mentioned as dreamers in "Let America be America Again" but Royalty living in the "Old World" was not mentioned to be a dreamer in the poem. Therefore, the answer is B. Royalty living in the "Old World".
While a subtitle can inform the reader of the topic of the text or give more information about the title, its main purpose is to be an extension of the title.
