In the above mentioned three sentences, the most appropriate sentence to be in the second position is Option A.
All the three sentences sync together, to describe about Mozart, the musical genius. While the first sentence speaks about an achievement which can only be dreamt of, the last sentence in the sequence speaks about a boy who proved this dream to be a reality, and is seen being leveled as a great musician. Thus, the second sentence is definitely mentioning the man, and his name as well, the third sentence refers to 'Mozart' with the antecedent 'he' which is only seen in Option A.
The other options B, C and D, explain such sequences as hypothetical and thus fail to fit in the second position.