The fact that is most helpful in understanding the themes in Charles Dickens's written work is:
D) When he was 12 years old, Dickens was forced to work in a factory, and it traumatized him.
This experience had a profound impact on Dickens and greatly influenced his writing, particularly his exploration of social justice, the plight of the poor, and the critiques of industrial society. Many of his works reflect themes of childhood struggles, the harsh realities of poverty, and the need for reform, which can be traced back to his own traumatic experiences during his youth.