这个解决方案在理论上是合理的，但不实用。

This solution is ___theoretically sound, but impractical.

理论上，有足够的食物给每个人，但饥饿问题依然存在。

___Theoretically, there is enough food for everyone, yet hunger persists.

他的论点在理论上是正确的，但在实际应用中失败。

His argument is ___theoretically correct, but fails in real-world applications.