In MLA documentation, to signify a quotation within a quotation, writers must:

A. use single quotation marks: "'I don't know,' Al said. 'I don't know what I want to eat'" (Hemingway 21).
B. use parentheses: "(I don't know,) Al said. (I don't know what I want to eat)" (Hemingway 21).
C. use asterisks: "*I don't know,* Al said. *I don't know what I want to eat*" (Hemingway 21).
D. use brackets: "[I don't know,] Al said. [I don't know what I want to eat]" (Hemingway 21).