Choice "A" is correct. When performing an attestation engagement related to a client's prospective financial statements, the accountant should ensure that the client discloses all significant assumptions that are used for the prospective financial statements. Choice "c" is incorrect. The client is not required to disclose the significant assertions used for the prospective financial statements, but must disclose the significant assumptions used. Choice "b" is incorrect. Pro forma financial statements are not required in an attestation engagement related to prospective financial statements. Choice "d" is incorrect. Historical financial statements are not required in an attestation engagement related to prospective financial statements.