Introduction:
In the story "The Selfish Giant" by Oscar Wilde, the man accepts the child's offer because it made him a free man. The story revolves around a giant who builds a wall around his beautiful garden to keep children out. As a result, the garden falls into perpetual winter, and the giant is left alone and unhappy. However, when a child enters the garden and the giant realizes the error of his ways, he undergoes a transformation.

Explanation:
- The child's offer to the giant is to allow him to play in the garden, and the giant accepts this offer eagerly. This acceptance leads to several significant changes in the giant's life, making option 'A' the correct answer.

Reasons for accepting the child's offer:
1. Freedom: The giant has been trapped in his own selfishness and isolation for a long time. By accepting the child's offer, he liberates himself from this self-imposed prison and experiences a newfound sense of freedom. The giant is able to roam and play in his garden, which brings him joy and fulfillment.

2. Redemption: The giant's initial decision to exclude the children from his garden was a selfish and heartless act. However, by accepting the child's offer, he realizes the error of his ways and seeks redemption. He acknowledges his past mistakes and strives to make amends by allowing the children back into the garden. This redemption brings about a positive change in the giant's character.

3. Transformation: The giant's acceptance of the child's offer leads to a transformative journey. He undergoes a significant change, both internally and externally. Initially, the giant is depicted as a selfish and cold-hearted character. However, through his interactions with the child and the other children who subsequently enter the garden, he learns the importance of love, kindness, and selflessness. This transformation makes him a better person and brings warmth and happiness back into his life.

Conclusion:
The man accepts the child's offer because it offers him freedom, redemption, and a transformative experience. By accepting this offer, the giant breaks free from his selfishness, finds redemption for his past actions, and undergoes a positive change in his character. The story emphasizes the importance of love, kindness, and selflessness in one's life, and the giant's acceptance of the child's offer is a pivotal moment in his journey towards personal growth and happiness.