Hey there!
When finding a characteristic of a memoir, we would find a
account or biography of a personal knowledge of a certain person.
From your option's above,a memoir would also be when you focus on a memory rather than the experience. Because, when you right about someone's (bio-ed) life, your have to remember what happened, not of the experience, it makes no sense, so that is why the last option's plugs in so well.
Your correct answer would be. . . .
Hope this helps.
~Jurgen