Answer:
The correct answers is: was.
Explanation:
During the 19th century, refers to <em>the past, </em>knowing that, it is possible to infer that the statement needs to be written in the past, the verb "to be" in the present is: <em>am, is, are </em>and in the past <em>was </em>and <em>were; </em>singular and plural. As Charles Dickens, is only one individual, we have to use <em>was. </em>If it was Charles Dickens and his friend... then we would use <em>were </em>(plural). So, it will read like this: During the 19th century, Charles Dickens was one of the most famous British novelists.