Final answer:
Sydney Carton's character development is best explained by his act of self-sacrifice to save Charles Darnay, demonstrating his redemption and the belief that his life can be meaningful.
Step-by-step explanation:
The best explanation for the development of Sydney Carton's character in Charles Dickens' A Tale of Two Cities option A: Sydney Carton sacrifices his life to prove his life is worth something. This is a pivotal moment in the novel that marks the culmination of Carton's character arc. Throughout the story, Sydney is depicted as a dissolute and depressed character with seemingly little value to society or to himself. However, his love for Lucie Manette inspires a profound transformation.
Initially, Sydney Carton does not fight for Lucie's love nor does he rush to Paris to save Gabelle specifically (these actions are taken by other characters). His problems with alcohol are part of his character, but they are not resolved in a way that is depicted as a major development of his character. Instead, his ultimate act of self-sacrifice by taking the place of Charles Darnay at the guillotine serves to demonstrate his redemption and his belief that his life can have a meaningful impact, confirming his earlier sentiment, 'It is a far, far better thing that I do, than I have ever done; it is a far, far better rest that I go to than I have ever known.'