In a quiz, I got wrong the following multiple choice question:
Wir bieten Ihnen wunderbares Bier an!
- — Welches?
- — Was für eins?
- — Was für welches?
I selected 2, while the correct answer is 3. Why is better to say welches? Or rather: why is it incorrect to say was für eins? I'm assuming that the interlocutor wanted to ask what kind (of beer) was offered.