Which of the following situations would provide an acceptable case for using a taxpayer's estimated figure in the preparation of a federal income tax return? Explain your answer.

a. The taxpayer has the necessary data available but is busy with a pressing public offering and has not had the time to look through her records for the information.

b. The data are not available at the time of filing the return, and the estimated amounts appear reasonable to the CPA.

c. The taxpayer has the data available at the time of filing the return but feels that the data do not fairly represent the results of her business operation and therefore desires to use an "estimate."

d. The taxpayer, relying on the income tax regulations that allow the use of reasonable estimates under certain circumstances, desires to use an estimate to determine the amount of his deduction for entertainment expenses.