Which of the Following Is Not a Skimming Scheme

Which of the following is not a skimming scheme?

A) Misappropriate customer payments and write off the receivable as "uncollectible'
B) Intercept checks intended for a third party and convert the checks to cash for their own use
C) Understate sales and collections by recording false or larger-than-reality sales discounts
D) Collude with customers so that they either pay later than required or less than required