3-How does the concept of duality apply of the characters in this novel?

From the very title of A Tale of Two Cities, Dickens signals that this is a novel about duality. Everything from the settings (London, Paris) to the people come in pairs. The pairs are occasionally related together. A crucial incidence of related doubling involves the resemblance between Charles Darnay and Sydney Carton, a similarity that drives the plot. The pairs are more often oppositional, just as in the dichotomous opening: "It was the best of times, it was the worst of times." For example, Lucie's physical and moral brightness is played off against the dark Madame Defarge.