Theoretically, the amount of estimated future returns and allowances on credit sales should be recorded during the period of the sale so as not to overstate sales and ending accounts receivable. In practice, these estimates are not recorded by most companies because A) the amount of such returns and allowances is usually not material. B) the amount of such returns and allowances tends to fluctuate too greatly from period to period. C) there is too much uncertainty surrounding such estimates. D) such estimates are not allowed according to generally accepted accounting principles