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.

The first option is the best and it also flows the smoothest.

The best way of combining sentences 1 and 2 is "Olaudah Equiano wrote a book, which was about his experiences as a slave and, later, as a free man".

Explanation: The best way of combining both sentences is by writing "Olaudah Equiano wrote a book, which was about his experiences as a slave and, later, as a free man" since it mantains the original meaning of the sentences. As the second sentence makes reference to the book, the second clause ("which was about his experiences as a slave and, later, as a free man") has been connected to the first one by means of the relative pronoun "which". The relative pronoun "which" is always used to provide additional information about the noun or pronoun that precedes it. Therefore, the original meaning of sentences 1 and 2 is kept. In contrast, the other combinations change their meaning by adding conjunctions ("even if", "until" and "although") that give another denotation to the sentence.  

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explanation: