regarding proper ethical accounting guidelines, which, if any, of the following is correct? a.if a client has made a mistake in a prior year's return and refuses to correct it, the accountant should withdraw from the engagement. b.if the exact amount of a deduction is not certain (e.g., around mid-$600s), it should be recorded as an odd amount (i.e., $649) so as to increase the appearance of greater certainty. c.the use of client estimates in preparing a return may be acceptable. d.under no circumstances should a question on a tax return be left unanswered.