MCQ risk

Mason also holds around $2 million of aircraft spares which are included within inventory. Mason sells the
aircraft spares to amateur flying associations. Aircraft spares which are not sold after three years are
scrapped.
Approximately a quarter of this value is made up of specialist equipment taken out of aircraft when it was
replaced by newer or more advanced equipment. Such specialist equipment is transferred from non-current
assets to inventory without adjustment, and continue to be recognised at amortised cost.
Which of the following summarises the key audit concern arising from the matter described?
A Accuracy, valuation and allocation of non-current assets
B Completeness of non-current assets
C Existence of inventory
D Accuracy, valuation and allocation of inventory

Sir correct answer is D. Please can you explain me this?