An auditors document includes the following statement:

Our audit is subject to the risk that errors, fraud, or illegal acts, if they exist, will not be detected. However, we will inform you of any such matters that come to our attention.

The above passage is most likely from

A comfort letter.

An engagement letter.

The explanatory paragraph of a compliance report on a government entity subject to GAO standards.

The explanatory paragraph of a subject to qualified auditors opinion.