An appraiser encounters an underground storage tank and there are no signs of failure. An appraisal could be performed under the presumption that the tank is not leaking. This would be an example of a(n)

extraordinary assumption

Explanation:

An extraordinary assumption often used in Real Estate, used under the Uniform Standards of Professional Appraisal Practice (USPAP), is a term that describes an assumption made about a condition or a fact which is barely unknown or uncertain. However, if later discovered to be untrue could change the resulting viewpoint or conclusion.

Hence, in this case, the correct answer is EXTRAORDINARY ASSUMPTION

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