what is answer for this question and why b cannot be the answer? i need an explanation to understand this question.

Thank you

15. Which one of the following is not an expense of the business in the current period? a) Sales taxes collected from customers and paid by the seller to the government tax office An estimate of the costs of a 2-year warranty provided to customers who have purchased goods in the current period c) Amounts owing to employees (but not yet paid) for work performed this period d) None of the above (all are expenses)