Which answer choice best states the difference between a memoir and a biography? a memoir contains imagery, but a biography does not. a memoir is fiction, but a biography is nonfiction. a memoir is written in first person, but a biography is written in third person. a memoir is written in third person, but a biography is written in first person.

It might be said that "A memoir is written in first person, but a biography is written in third person" (option C) A memoir is a kind of autobiography that involves an author´s public life. it is about personal knowledge and experiences that is why it is written in first person. The biography might be written in 3rd person which might include details of public and private life. 

The correct answer is
A memoir is written in first person, but a biography is written in third person.

Memoirs are written in the first person because they are true recollections of the life of the person who is writing them. They are talking about their life. Biographies are written about someone else, like a writer writing about a famous person, so it's in the third person.