State whether each of the following is an accounting policy or an accounting estimate for Company A:
(a) The useful life of depreciable plant is determined as being six years.
(b) Company A recognises income arising from service contracts on the basis of the stage of completion.
(c) Company A determines that it will calculate its warranty provision using past experience of defective products.
(d) The current year's warranty provision is calculated by providing for 1% of current year sales, based on last year's warranty claims amounting to 1% of sales.