Letter A is correct.
Even though Jesus was very obedient to his parents, that would not be a strong enough evidence for James to believe that He was the Christ. Also, Jesus did NOT perform miracles when he was a young child. In fact, the bible says his first miracle happened at a wedding (where he was already a grown man) and transformed water into wine. As a matter of fact, Jesus' relationship with God was a good indicator that He was the Christ. However, the story of Jesus' unusual birth was the strongest evidence and confirmed the prophecies and scriptures that had already been written in the Old Testament.