The phrase "a single answer but" is not correct and does not convey a complete thought in written English.
It may be used in a context where you want to introduce a contrast or exception to the idea of having a single answer, but it requires additional information to be clear.
Example: "There may be a single answer but it is not the only perspective to consider."
Alternatives: "one answer, yet" or "a sole response, however".
"We know people want a single answer, but it just does not work out as simply as that.
Watson, he added, is not going to make diagnoses, not give a physician a single answer, but make suggestions, recommendations and determine probabilities.
The archbishop won't be able to answer that question in a single word, nor can there be a single answer; but he should be better qualified than most people to help us wrestle with that dilemma.
These problems are not straightforward — neither poverty nor racism nor the depredations of popular culture represent a single answer — but Obama, as a high-school teacher, could reinvigorate efforts to solve them.
I have been approached by many young composers wanting to write opera, and the first question I always ask is: 'What is your favourite play and who is your favourite playwright?' I'm never expecting a single answer, but an answer is essential.
This is because questions typically have only a single answer but it is possible to ask multiple questions that all lead to the same answer.
Regarding their abrupt breakup, a single answer is elusive, but they said Mr. Damiani's departure from the band shortly before the Beatles tour seriously affected the mood, and that witnessing the Fab Four's intense fame perhaps had an adverse effect.
There are plenty of ways to greet somebody, for example, but most services will often only accept a single answer.
It is not one answer or the other, but each reciprocally answering the other, never settling on a single "Answer".
But a group of engineers at IBM think they have a single answer to both problems.
