Read this passage from "How a Cat Played Robinson Crusoe." When spring came back to the island, with the nightly shrill chorus of frogs in the shallow pools, and the young grass alive with nesting birds, the prisoner's life became almost pleasant in its easy abundance. But now she was once more homeless, since her snug den had vanished with the snow. This did not much matter, however, for the weather grew warmer and more tranquil day by day. And she herself, in being forced back upon her instincts, had learned to be contented. Nevertheless, with all her capacity for learning and adapting herself, she had not forgotten anything.
One theme of this story is "Necessity is the mother of invention." How does the sentence "And she herself, in being forced back upon her instincts, had learned to be contented" help to develop this theme?

A The cat is proud of how little she needs to feel comfortable now.
B The cat is happy now that the family is gone and she has the house to herself.
C The cat was used to hunting for her own food, so her instincts were always there.
D The cat was used to being cared for, so she had to learn how to survive on her own.