Answer:
The correct answers is: was.
Explanation:
During the 19th century, refers to the past, 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: am, is, are and in the past was and were; singular and plural. As Charles Dickens, is only one individual, we have to use was. If it was Charles Dickens and his friend... then we would use were (plural). So, it will read like this: During the 19th century, Charles Dickens was one of the most famous British novelists.
