You will have to post the story and make your question more clear, otherwise people will not answer.
C. He has come to believe that there are no consequences for bad behavior
I'd say that the third sentence, "We'd watch Shirley's old movies on TV as though they were training films" shows that the mother knows "how" her daughter can become a prodigy.
The first sentence just compares the girl to Shirley Temple, but doesn't show that the mother knows how the daughter can become a prodigy, just that she could be.
And the second sentence is just a description of their dining habits.
The last sentence is a very general statement that does not indicate that the mother knows how the child could possibly become a prodigy. Therefore, the second sentence is correct because it shows them watching the Shirley Temple videos like "training videos", which would help the girl become a prodigy.
I hope this helped.