Hmm…This question is tricky! The answer is B. I went back to my FAR materials and it states that if inseparable, it is treated as accounting estimate. I sent technical question to customer support.
Anyway, I googled it and this is what I found:
SFAS no. 154 par. 20. – “…are considered changes in estimates for purposes of applying this Statement.”.
AU-420.13 – “The effect of a change in accounting principle may be inseparable from the effect of a change in estimate. Although the accounting for such a change is the same as that accorded a change only in estimate, a change in principle is involved. Accordingly, this type of change requires recognition in the independent auditor's report through the addition of an explanatory paragraph…”
AU-C 708.A10 – “Paragraph .10 requires the auditor to evaluate and report on a change in accounting estimate that is inseparable from the effect of a related change in accounting principle like other changes in accounting principle…”
So I guess answer B is correct because that's based on auditing standards not accounting standards. Interesting!