B is corrent because while an attestation engagement will always have subject matter, it sometimes will not have a written assertion. For example, consider a situation in which the CPA’s client is not responsible for the subject matter; in such a circumstance it may not be possible to obtain a written assertion from the individual who is the responsible party.
A is incorrect because one of the replies is incorrect.
C is incorrect because one or both of the replies are incorrect.
D is incorrect because one of the replies is incorrect.
