Sergei's refusal to answer the question shows he doesn't know what to say.
We can arrive at this answer because:
Sergei acknowledges his responsibility, he doesn't want to spend the wish on someone else, but he has nothing to justify keeping the wish and so he doesn't respond.
This question is about "What, of this Goldfish, Would You Wish?" and you can find more information on this short story at the link:
https://brainly.com/question/2095002