Answer:
One day, as two white doves suddenly soared aloft in the blue sky, the poor little bird, who had now become the prince's comrade, gave a pitiful little trill.
Step-by-step explanation:
A. The next day, as he was carefully cleaning the bird's cage, the walls again creaked and groaned, and the mirrors grew narrower as the windows widened.
-The words in this option suggest that doing good things or helping others did the exact opposite, only brought mischief to oneself. So this is incorrect.
B. His fairy godmother had told him that it was his house; therefore he was interested in looking at everything in it.
-No words in this suggest either, no words suggest the theme that helping others often brings benefits to oneself. So this is incorrect.
C. One day, as two white doves suddenly soared aloft in the blue sky, the poor little bird, who had now become the prince's comrade, gave a pitiful little trill.
I think this would be correct if the bird was sacrificing his own happiness for the sake of the two doves, because at the end he gave a pitiful trill. But, we don't really know that, so I think it would be wrong but lets just assume that's what its doing so I say this is correct.
D. He spent so much time gazing into the wonderful mirrors that he had very little use for the books and games that had been placed there for him.
He had been given gifts of books and games, but had no use of them because he was gazing into the mirrors. I don't really see how this has to do with the theme. So. I am going with incorrect.
If I am wrong please tell me so, option C just makes the most sense.