What made the pillow book unique?
it was a book many japanese women used to learn to read and write japanese.
it was one of the first books in japan written by a woman, sei shonagon.
it was the first book of tanka poetry written by yamanoue no okura.
it was the first book written by a woman to be classified as literature.

If you look up the Pillow Book, it was written by Sei Shonagon and is a book about her observations of Japanese court life. So you can definitely rule out A and C as they are blatantly wrong

I would say B is the correct answer

It could be D instead to be honest, but since it's more of a memoir - might not be classifed as literature. The first book written by a woman that COULD be classified as literature is the Tale of Genji published around the same time as the Pillow Book, also in Japan.

Historians are not 100% sure which one was printed first anyway