Read the sentences.
[1] Olaudah Equiano wrote a book. [2] It was about his experiences as a slave and, later, as a free man.
Which is the best way to combine sentences 1 and 2?
Olaudah Equiano wrote a book, which was about his experiences as a slave and, later, as a free man.
Olaudah Equiano wrote a book, even if it was about his experiences as a slave and, later, as a free man.
Olaudah Equiano wrote a book, until it was about his experiences as a slave and, later, as a free man.
Olaudah Equiano wrote a book, although it was about his experiences as a slave and, later, as a free man.