Answer: A. tried as far as possible to pretend there was nothing burdensome about it
Explanation: Trying as far as possible to pretend there was nothing burdensome about "it" would best support Grete's new attitude towards her brother Gregor. He had not been able to reach out to his sister to at least discuss whatever had happened and that had been a great bother to him, even though Grete fared better by not talking about it.